GB2553855A

GB2553855A - Radio transmitter detection

Info

Publication number: GB2553855A
Application number: GB1615941.0A
Authority: GB
Inventors: Babayev Bagtiyar
Original assignee: Individual
Current assignee: Individual
Priority date: 2016-09-19
Filing date: 2016-09-19
Publication date: 2018-03-21
Also published as: GB201615941D0

Abstract

The invention relates to alert apparatus for monitoring radio frequency transmissions from a transmitting device. An alert apparatus 100 receives an RF signal, from transmitting device, through an antenna and filters the signal to block RF signals above a predetermined frequency but pass RF frequencies below the predetermined frequency. When the filtered RF signal is determined to exceed a threshold duration an alert indication is sent to a user. Preferably the alert indication takes the form of a telephone call from the alert apparatus to a cellular phone of the user. The threshold frequency may be 800MHz or any other frequency which ensures cellular communications are blocked but walkie-talkie communications are passed.The alert indication that signals are being transmitted within range of the alert apparatus which are likely to carry speech and are likely to have been transmitted by a handheld transceiver such as a walkie-talkie. A claim to a computer program omits the filtering, antenna and RF requirements. The issuing of an alert may also be conditional on the filtered RF signal exceeding a power threshold.

Description

(71) Applicant(s):

Bagtiyar Babayev

Rose Walk, ROYSTON, Hertfordshire, SG8 5HG, United Kingdom (72) Inventor(s):

Bagtiyar Babayev (56) Documents Cited:

EP 1701526 A1 WO 2015/124689 A

US 4833725 A US 0590335 A

US 20100056207 A1 US 20050085252 A1 (58) Field of Search:

INT CL H04B, H04L, H04M, H04W Other: Online: WPI, EPODOC (74) Agent and/or Address for Service:

Snipe Chandrahasen LLP

Kingsland Road, London, E2 8AA, United Kingdom (54) Title of the Invention: Radio transmitter detection

Abstract Title: Alerting a user to RF transmissions of a duration which exceeds a threshold duration (57) The invention relates to alert apparatus for monitoring radio frequency transmissions from a transmitting device. An alert apparatus 100 receives an RF signal, from transmitting device, through an antenna and filters the signal to block RF signals above a predetermined frequency but pass RF frequencies below the predetermined frequency. When the filtered RF signal is determined to exceed a threshold duration an alert indication is sent to a user. Preferably the alert indication takes the form of a telephone call from the alert apparatus to a cellular phone of the user. The threshold frequency may be 800MHz or any other frequency which ensures cellular communications are blocked but walkietalkie communications are passed.The alert indication that signals are being transmitted within range of the alert apparatus which are likely to carry speech and are likely to have been transmitted by a handheld transceiver such as a walkie-talkie. A claim to a computer program omits the filtering, antenna and RF requirements. The issuing of an alert may also be conditional on the filtered RF signal exceeding a power threshold.

FIG. 3A

1/4

k—

2/4

118

106

112

114

FIG. 2

100

3/4

FIG. 3A

4/4

Retrieve phone number and initiate call set up

212

Communications network sets up call

Receive an indication that the communication device of the user is ringing

216

FIG. 3B

Signal is converted from analogue to digital

218

RADIO TRANSMITTER DETECTION

Field of the Invention

The invention relates to a method of and apparatus for determining that a received RF signal is likely to have been transmitted by a handheld portable radio transmitter and is likely to be carrying speech, and indicating such to a user. The invention also relates to a related computer program.

Background

Portable handheld radio transceivers, often known as walkie-talkies, may be used for communication with other handheld radio transceivers operating on the same radio frequency and within communications range. Such radio transceivers may be used when outside the coverage of cellular telecommunications networks. For example, such radios may be used between members of a group when in remote areas. Activities in such areas may be sports related, such as hiking, cycling, skiing and hunting. Such radio transceivers may also be used by people working in areas where they do not have access to the local cellular telecommunications networks, for example by military personnel working in war zones. Portable handheld radio transceivers may also simply be used between persons who do not wish to pay for access to a cellular telecommunications network.

Portable handheld radio transceivers also enable communication without a record of the communication being made. In contrast, data on communications over cellular telecommunications networks are generally retained by the service provider. Such data typically comprise, for each call or SMS message, at least: a number of a calling or sending device, a number of a receiving device, a time and call duration, and location information. The location information is at least identifiers of base stations via which the sending and receiving devices are communicating. Use of portable handheld radio transceivers is thus attractive to persons who wish to communicate while carrying out criminal activity.

There are good reasons for wanting to detect if communication via portable handheld radio transceivers is taking place. For example, it may be wanted to detect if hunters are communicating locally, or if persons who wish to communicate clandestinely are present in a particular area. It is an object of the present invention to provide a solution.

Summary of the Invention

In accordance with a first aspect of the present invention, there is provided apparatus comprising: an antenna means for receiving RF signals; a controller means; a filter means coupled to the antenna means and to the controller means, the filter means being for blocking RF signals at frequencies above a threshold frequency from reaching the controller means, wherein the controller means is configured to determine if a duration of a non-blocked RF signal exceeds a threshold duration, and based at least on a determination that the duration is exceeded, to cause sending of an alert indication to a predetermined user.

The user is thus alerted to the likelihood that someone is using a handheld radio transceiver near where the RF signal is received. The indication is typically received by a communications device of the user. The user may be alerted in real-time if the user is monitoring the device, or becomes aware when viewing the device. The threshold duration is such that the RF signals of duration less than the threshold duration would be unlikely to carry speech.

The controller means is preferably configured to determine information indicative of the power level of the non-blocked RF signal exceeding a threshold level, and to cause the sending of the alert indication based on at least a determination that the duration of the RF signal exceeds the threshold duration and over this duration the information indicates that the power level of the non-blocked RF signal has exceeded the threshold level.

Frequencies above the threshold frequency may include those typically used for communication by GSM networks. The filter means may be configured to block at least signals at frequencies above 800MHz from reaching the controller means. This would result in frequencies typically used by GSM networks being blocked. The filter means may be configured to block at least signals at frequencies above 500MHz from reaching the controller means.

The threshold duration may be configurable. The threshold level may be configurable. These allow the sensitivity of the apparatus to be adjusted.

The apparatus may further comprise an amplifier operatively coupled to the controller means and the filter means. The amplifier may be configured to convert the signal to a direct current signal in which the voltage level represents the power level of the RF signal, before the signal is received at the controller means.

The apparatus may further comprise communications means operatively coupled to the controller means. The communications means may be configured to communicate with a cellular telecommunications network to cause sending of the alert indication, where the controller means causes the communications means to initiate a call using the cellular communications network.

There may be further provided a system comprising: a plurality of units, each comprising any of the above described apparatus; and a communications device under the control of the user, configured to receive alert indications from each of the units, wherein received alert indications are individually identifiable at the communications device as having been sent by a particular one of the units.

According to a second aspect of the present invention, there is provided a method comprising: receiving RF signals; blocking received signals at frequencies above a threshold frequency; determining for each signal below the threshold frequency if a duration of the RF signal exceeds a threshold duration; based on a result of the determining being that the duration is exceeded, causing sending of an alert indication to a predetermined user.

According to a third aspect of the present invention, there is provided a computer program comprising computer program code stored in a memory means, which, when run on a processing means, is configured to perform the steps of: determining for a received signal if a duration of the signal exceeds a threshold duration; based at least on a result of the determining being that the threshold duration is exceeded, causing sending of an alert indication to a predetermined user.

Optional and/or preferred features or steps in accordance with the second and third aspects of the invention are set out in the dependent claims.

Brief Description of the Figures

For better understanding of the present invention, embodiments will now be described, by way of example only, with reference to the accompanying Figures in which:

Figure 1 shows illustratively an RF alert unit in accordance with an embodiment of the invention in an environment in which the RF alert unit may be implemented;

Figure 2 shows diagrammatically elements of the RF alert unit;

Figures 3A and 3B are a flowchart indicating steps that occur when the RF alert unit receives a signal transmitted by a handheld radio transceiver;

In embodiments of the invention, RF (radio frequency) signals are received and filtered to remove signals that are unlikely to have been transmitted by two-way handheld radio transceivers, such as walkie-talkies. Signals that are likely have been transmitted by such radio transceivers are processed and monitored to determine whether they are likely to carry speech. If it is determined that a signal is likely to carry speech, an alert indication is then sent to a predetermined user.

Referring to Figure 1, first and second handheld radio transceivers 10 and 12 enable two-way communication. An RF alert unit 100 is located so that RF signals transmitted by at least one of the first and second radio transceivers 10 and 12 are detectable by the RF alert unit 100. In addition, the RF alert unit 100 is in the coverage area of a base station 16 of a cellular telecommunications network.

Referring to Figure 2, the RF alert unit 100 includes detection circuitry and alerting circuitry, both including a common microcontroller 102. The detection componentry' comprises a first antenna 104, a low-pass filter 106 and a logarithmic amplifier 108, in addition to the microcontroller 102. The microcontroller 102 includes an embedded analogue-to-digital signal converter (ADC) 110.

Handheld radio transceivers typically transmit in the very high frequency (VHF) band and the ultra-high frequency (UHF) band, with the majority transmitting at frequencies between 100MHz and 500MHz. The first antenna 104 is configured to receive RF signals including those between 100MHz and 500MHz. The first antenna 104 may be configured to receive signals from about 27MHz to 500MHz, in which case the first antenna 104 may have to be longer than if only signals having frequencies above 100MHz are to be received.

The low-pass filter 106 is connected to the first antenna 104 and to the logarithmic amplifier 102. Since the signals received at the first antenna 104 may include frequencies above 500MHz, the low-pass filter 106 is configured to block signals above 500MHz from proceeding to the logarithmic amplifier 108.

The frequency ranges at which GSM mobile phones operate are between about 380.2 MHz and 1989.8 MHz, which includes frequency spectrum for both transmission from mobile phones to base stations and from base stations to mobile phones. However, most communication is in bands GSM-900 and DCS-1800, whose frequencies are all above 800MHz. Thus the cut-off frequency of the low-pass filter 108 is effective at preventing the logarithmic amplifier 108 from receiving cellular telecommunications network signals. The cut-off frequency of the low-pass filter 106 does not need to be 500MHz and may be different in variant embodiments. In some variant embodiments, the cut-off frequency may be about 800MHz. In addition, in some embodiments RF signals received below a threshold frequency, for example 100MHz, may be blocked. This may be implemented by replacing the low-pass filter with a suitable band-pass filter.

The logarithmic amplifier 102 is configured to provide a DC (direct current) output signal having a voltage corresponding to the amplitude of the received RF signal, and to send the DC output signal to the microcontroller 102. A voltage value of the output DC signal is thus representative of the power level of the received RF signal.

The microcontroller 102 is configured to receive the DC output signal, which is then processed by the ADC 110. The ADC 110 is configured to sample the DC output signal, thereby to convert the DC to a digital signal. Values of the digital signal are compared to a threshold value for power level stored in a memory of the microcontroller 102. The threshold power level value may be set by the user.

If the threshold power level value is exceeded, the microcontroller 102 is configured to then measure the duration of the signal. The microcontroller 102 is configured to monitor the duration over which the received signal is received and has a power level greater than the threshold power level value. The microcontroller 102 is configured to determine if the duration is greater than a threshold duration, which may, for example 10 seconds, and may be set by the user. A duration greater than the threshold duration, and the power level being greater than the threshold power level value are indicators of the received signal carrying speech. If the duration is less than the threshold duration, it is assumed that the signal does not carry speech. Notably, it is not relevant whether the speech is encrypted or not.

Further to determining that the duration of a received signal is greater than a threshold duration, the microcontroller 102 is configured to cause an alert indication to be sent to a predetermined user.

The alerting componentry comprises a cellular communications module 112, a second RF antenna 114 and a subscriber identification module (SIM) card 116. The cellular communications module 112 is operatively connected to the microcontroller 102, to the second antenna 114 and to the SIM card 116.

The SIM card 116 is registered with a service provider of cellular telecommunications network services and has a unique telephone number associated with it, in a conventional way. The SIM card 116 is not limited to any particular kind of SIM card. Although not commonplace now, it is possible that the functionality of the SIM card may be integrated into the cellular communications module 112. The cellular communications module 112 is registered with the cellular telecommunications network when the RF alert unit 100 is turned on. Thus, the cellular communications module 112, the second antenna 114, and the SIM card 116 together enable calls to be made to a recipient device via the cellular telecommunications network.

The SIM card 116 is configured with memory locations at which telephone numbers can be stored. A recipient telephone number is stored in a first memory location on the SIM card 116. The microcontroller 102 is configured, in response to determining that received signal has a greater duration than the threshold duration, to instruct the cellular communications module 112 to access the telephone number in the first memory location and to initiate a call to the telephone number using the second antenna 114 to transmit a calling signal to the cellular telecommunications network

14.

The RF alert unit 100 includes a battery 118, which may be a lithium ion battery. The battery 118 is connected to the microcontroller 102 and supplies power to the RF alert unit 100. The RF alert unit 100 also includes an operatively connected power button, enabling the RF alert unit 100 to be turned on and off.

Although not indicated in the Figures, the battery 118 is rechargeable. Preferably, the RF alert unit 100 includes a USB port or micro USB port connected to the battery 112, together with suitable power control circuitry, so that the battery can be connected to an external power source for charging. For example, the port may be connectable to a mains power supply or to a USB port of a computer. In a variant embodiment, the battery 118 is absent and the RF alert unit 100 is connected to a mains power supply when in use.

Operation of the RF alert unit 100 will now be described with reference to Figure 3 A, when the handheld radio transceiver 10 and the RF alert unit 100 are sufficiently close that the signal that the RF alert unit 100 receives is of sufficient strength for operation, and when the transmitted signal is below the cut-off frequency of the low-pass filter 106.

First, at step 200, the signal is received at the first antenna 104 and proceeds to the low-pass filter 106. Since the signal is below the cut-off frequency, the signal passes through the low-pass filter 106 to the logarithmic amplifier 108 at step 201. If the signal were above the cut-off frequency, the signal would be blocked.

At step 202, the logarithmic amplifier 108 converts the RF signal to a DC output signal and the DC signal proceeds to the microcontroller 102. At step 204, the ADC 110 samples the received DC output signal to convert the received signal to a digital signal.

At step 205, the microcontroller 102 monitors a voltage level of the digital signal. If the voltage level exceed a threshold voltage level, indicating that the power level of the received RF signal is greater than a threshold power level, the microcontroller 102 begins monitoring the duration of the digital signal (step 206). If the microcontroller 102 determines that the threshold power level value has been exceeded for a time period greater than the threshold duration at step 208 (indicating a possible speech transmission as opposed to a glitch), the microcontroller 102 sends an instruction to the cellular communications module 112 to initiate a call at step 210.

Turning to Figure 3B, in response to receiving the instruction from the microcontroller 102, the cellular communications module 112 retrieves the telephone number from the first memory location on the SIM card 116 and begins call set up signalling via the base station 16 of the cellular communications network, the base station 16 being within communications range of the RF alert unit 100, at step 212. In the call set up signalling, the telephone number for the SIM card 116 is sent to the cellular telecommunications network 14.

The cellular telecommunications network 14 then handles call set up using the retrieved telephone number in a conventional way at step 214. A detailed description of call set up are beyond of the scope of the present disclosure. The cellular communications module 112 receives from the cellular telecommunications network 14 a signal indicating that a communications device is ringing 216 and sends a signal indicating this to microcontroller at step 216. After a predetermined period has passed, for example five seconds, the microcontroller 102 signals to the cellular communications module 112, to end of the call at step 218.

Typically, the recipient communications device that is called, that is, the device whose number is stored in the first memory location of the SIM card 116, is a conventional mobile phone. In this case, and although not essential to embodiments, the communications device is capable of maintaining a record of missed calls, the telephone number of the caller, and the date and time of the call.

Preferably, the communications device has the telephone number associated with the SIM card 116 stored in as a contact. In any case, the user of the recipient communications device is able to understand that the call received is from the RF alert unit 100. Since the user will be aware of the function of the RF alert unit 100, it will be understood by the user that the RF alert unit 100 has detected an RF signal that is likely to carry speech and to have been generated by a handheld radio transceiver in the vicinity of the RF alert unit 100. Typically the user is also aware of the location of the RF alert unit 100, meaning that the user is aware of the area in which a transmission using a radio transceiver is taking place.

The user may hear the communications device ringing when the RF alert unit 100 calls it and become aware of the RF signal transmission in real-time. Alternatively, the recipient device may review one or more missed calls from the RF alert unit 100 at a later time.

It is preferred that the call from the RF alert unit 100 is not answered by the user or by voicemail to avoid incurring of costs with the service provider. Preferably, if the call is answered, the microcontroller 102 is configured to instruct the cellular communications module 112 to end the call.

As will be appreciated by the skilled person, while simplicity is preferred by the inventor, the RF alert unit 100 could be modified to send voice messages or SMS messages.

Many modifications can be made to the embodiments described above within the scope of the present invention. The RF alert unit 100 may be modified to make call to multiple telephone numbers in response to determining that there is a likelihood of the received signal carrying speech. In this case, the SIM card 116 is configured with multiple telephone numbers each stored in a respective memory location on the SIM card 116 and the microcontroller 102 is configured to control the cellular communications module to call each of the number in turn.

Preferably, after a call has been made by the RF alert unit 100, the microcontroller 102 is not configured to cause any calls to be placed to the user until a predetermined period has passed, for example five minutes. This is to avoid repeated calls to the user in quick succession. Also, the microcontroller 102 is preferably configured to continue monitoring a signal in relation to which a call has been placed after the call has been placed and, where that signal is continuously received, not to place a further call in response to that particular signal.

Where it is desired for a greater geographical area to be monitored for RF signals from handheld radio transceivers that are likely to be carrying speech that can be achieved with the RF alert unit 100 described above, multiple such units may be distributed over the geographical area. Each unit 100 has a respective SIM card, each of which is registered with a particular service provider and has a unique telephone number assigned to it. Preferably, each SIM card 116 has the same telephone number stored in a first location thereof. The communications device of the user, to which the telephone number corresponds, preferably has each telephone number, together with an identifier of the respective RF alert unit, stored as contacts. This means that the user of the communications can associate missed calls from the RF alert units each with a particular one of RF alert units. Since the user will typically be aware of the location of each RF alert unit, the user will thus be aware of the approximate location of the transceiver radio that transmitted the signal that resulted in the missed call.

Where multiple RF alert units are employed, the RF alert units will respectively call the communications device when an RF signal is received and determined to be likely to be carrying speech. Thus, the recipient device may receive multiple calls. In practice, the user may find that the communications device lists alert indications in the form of missed calls from identified RF alert units, together with times and dates of the missed calls.

Aspects of the set up of the RF alert unit 100 will now be described. The threshold duration over which a received signal must be monitored before an alert indication is transmitted may be configurable or preset. The threshold power level value that the power level of a non-blocked RF signal must exceed during the duration may also configurable or preset. As will be appreciated by the skilled person, there are various ways in which the microcontroller 102 may be programmed with the thresholds. In a preferred embodiment, the RF alert unit 100 has an FED (not shown) operatively coupled to the microcontroller 102. The microcontroller 102 is preconfigured to allow any one of 10 threshold durations to be set by the user. Initially, the power button is depressed by the user until the FED lights up. The power button is then depressed by the user between one and 10 times. The greater the number of times the power button is pressed, the lower the threshold duration. The microcontroller 102 is configured to store the threshold level that is set. The number of possible threshold durations with which the microcontroller 102 is preconfigured may be greater or fewer than 10. The user may experiment with different threshold levels, as the particular threshold level chosen may affect the sensitivity of the RF alert unit 100. Where the sensitivity is high, a greater number of calls may be initiated by the microcontroller 102 in error. The power threshold level value may be set in the same way, save, in an embodiment, the power button may be depressed three times in quick succession to instruct the microcontroller 102 that power threshold level configuration is to take place.

The RF alert unit 100 may be turned on using the power button, by pressing it once briefly and releasing it. In embodiments, the microcontroller 102 is usefully configured, in response to being turned on, to cause the FED to flash a number of times corresponding with the level between one and 10 at which the threshold level is set.

After the RF alert unit 100 has been turned on, the cellular communications module 112 is configured to register with the cellular communications network. Preferably, the cellular communications module 112 is configured to cause the another FED, which is operatively connected to the cellular communications module, to flash, while the registration is taking place. After registration has taken place, flashing of the red LED slows or stops. If this other LED continues to flash at the same rate, this indicates that either the RF alert unit 100 is not within coverage of the cellular communications network or there is a problem with the registration with the network.

The microprocessor 102, typically has spare input/output ports and spare memory. Thus, a display and/or other functionality, may be easily added.

In an embodiment in which life of the battery 124 is extended, the cellular communications module 102 is powered only when a call is to be placed. This has the drawback that the cellular communications module 102 must register with the cellular communications network before the call can be placed, leading to a delay.

The microcontroller 102 includes a processor, a memory including RAM and program memory, an oscillator, a timer and input/outputs, as well as the ADC 110, all operatively connected in a conventional way. The memory has a computer program stored in it which, when execute by the process, enables the functionality ascribed to the microprocessor 102 herein to be performed.

The applicant hereby discloses in isolation each individual feature or step described herein and any combination of two or more such features, to the extent that such features or steps or combinations of features and/or steps are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or steps or combinations of features and/or steps solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or step or combination of features and/or steps. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1. Apparatus comprising:

an antenna means for receiving RF signals; a controller means;

a filter means coupled to the antenna means and to the controller means, the filter means being for blocking RF signals at frequencies above a threshold frequency from reaching the controller means, wherein the controller means is configured to determine if a duration of non-blocked RF signal exceeds a threshold duration, and based at least on a determination that the duration is exceeded, to cause sending of an alert indication to a predetermined user.

2. The apparatus of claim 1, wherein the controller means is configured to determine information indicative of the power level of the non-blocked RF signal exceeding a threshold level, and to cause the sending of the alert indication based on at least a determination that the duration of the RF signal exceeds the threshold duration and over this duration the information indicates that the power level of the non-blocked RD signal has exceeded the threshold level.

3. The apparatus of claim 1 or claim 2, wherein frequencies above the threshold frequency includes those typically used for communication by GSM networks.

4. The apparatus of any one of the preceding claims, wherein the filter means is configured to block at least signals at a frequency above 800MHz from reaching the controller means.

5. The apparatus of claim 4, wherein the filter means is configured to block at least signals at a frequency above 500MHz from reaching the controller means.

6. The apparatus of the preceding claims, wherein the threshold duration is configurable.

7. The apparatus of any one of the preceding claims, wherein the threshold level is configurable.

8. The apparatus of any one of the preceding claims, further comprising an amplifier operatively coupled to the controller means and the filter means, wherein the amplifier is configured to convert the received signal to a DC signal before the signal is received at the controller means, wherein the voltage of the DC signal is indicative of the power level of the received RF signal.

9. The apparatus of any one of the preceding claims, further comprising communications means operatively coupled to the controller means, the communications means being configured to communicate with a cellular telecommunications network, wherein, to causing sending of an alert indication, the controller means causes to the communications means to initiate a call using the cellular communications network.

10. A system comprising:

a plurality of units, each comprising the apparatus of any one of claims 1 to 9 ; a communications device under the control of the user, configured to receive alert indications from each of the units, wherein received alert indications are individually identifiable at the communications device as having been sent by a particular one of the units.

11. A method comprising: receiving RF signals;

blocking received signals at frequencies above a threshold frequency; determining for each signal below the threshold frequency if a duration of the RF signal exceeds a threshold duration;

based on a result of the determining being that the duration is exceeded, causing sending of an alert indication to a predetermined user.

12. The method of claim 11, further comprising:

determining information indicative of the power level of the non-blocked RF signal exceeding a threshold level, wherein the causing the sending of the alert indication is further based at least on a determination that the duration of the RF signal exceeds the threshold duration and over this duration the information indicates that the power level of the nonblocked RD signal has exceeded the threshold level.

13. The method of claim 11 or claim 12, wherein frequencies above the threshold frequency includes those typically used for communication by GSM networks.

14. The method of any one of claims 11 to 13, wherein the threshold frequency results in signals at frequencies above 800MHz being blocked.

15. The method of claim 14, wherein the threshold frequency results in signals at frequencies above 500MHz being blocked.

16. The method of any one of claims 11 to 15, wherein the threshold duration is configurable.

17. The method of any one of claims 11 to 16, wherein the threshold level is configurable.

18. The method of any one of claims 11 to 17, further comprising converting a received non-blocked signal to a DC output signal before the determining if a duration of the RF signal exceeds a threshold duration

19. The method of any one of claims 11 to 18, wherein, the causing sending of an alert indication comprising causing a communications means to communicate with a cellular telecommunications network to initiate a call using the cellular communications network.

20. A computer program comprising computer program code stored in a memory means, which, when run on a processing means, is configured to perform the steps of:

determining for a received signal if a duration of the signal exceeds a threshold duration;

based at least on a result of the determining being that the threshold duration is exceeded, causing sending of an alert indication to a predetermined user.

21. The computer program of claim 20, further configured to determine 5 information indicative of the power level of the non-blocked RF signal and of the power level exceeding a threshold level, wherein the causing the sending of the alert indication is further based at least on the information indicating that the power level exceeds the power level for the duration.

10

22. The computer program of claim 20 or claim 21, wherein the threshold duration is configurable.

23. The computer program of any one of claims 20 to 22, wherein the threshold level is configurable.

24. A method, apparatus, computer program or system substantially as hereinbefore described with reference to the accompanying drawings.

Intellectual

Property

Office

Application No: GB1615941.0 Examiner: Dr John Cullen