Mobile phone signal Detector

I want to know if there is any 'mobile phone signal detector' already available in the market.

The purpose is to find if anybody is using mobile phone for calls or messaging at restricted places. Jammers are not fine as some are exempted from making calls etc..

If there is nothing like that available, how to make one to detect the signal or even the phone from which the signal was emitted.
Usually when we are about to receive a call or sms and if we are near a Speaker we get a specific noise through speaker, or if we are near a monitor (CRT) it flickers.  So I am sure there are ways to find this signal emission.

Please suggest the options to do this....

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FlipFlop4 years ago
Try the following link. I've built this circuit on breadboard and it works great, just pay attention to lead configuration of capacitor C3 in this circuit. I used just a five inch long wire(from a network cable Cat5 or Cat6) as an antenna. With 12 Volt power supply it's sesitivity increases too much so I used a 9 volt battery, I'm sure one can use a 9 volt power supply aswell. This circuit is actually from Electronics For You an Indian magazine. Here is the link.


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donjoy (author) 6 years ago
Thank you so much for the detailed explanation..
So from what you all say I feel

--The only possibility is we can detect if there are any phones in the area which is on call.
--As I understand from what NachoMahma said, the method to pin point 'the phone in use' may be illegal.

My last question on this to you all..

? When we keep the phone near a speaker, we dont hear any noise till there is some call or sms we receive. If the phone is emitting signal all times why are we not hearing that sound/noise always?
Same case with monitors. Only when there is a call or sms it flickers.

According to this, what I feel is there may be an increase in the radiation emitted when the phone receives a call or sms -right?

kelseymh donjoy6 years ago
Your last question is one I've had myself many times. My wife and I have different phones and different services, and our experiences are surprisingly different. Her phone causes speaker interference all the time -- every few minutes you get that annoying "bzzzzz---bz-bz-bz-bz". Mine only does that when someone calls me, and even then, not every time.

I suspect there's a strong dependence on the communication system and frequency/ies, which depend on the service provider and the phone.
donjoy (author)  kelseymh6 years ago
Ok Thank you for this info too :) So its again dependent on the provider. Anyway I'll do further research on this in some other website. Nice to have such good response from both of you..Thank you !!!
.  You may do better by asking your question on a site more specific to cell phones.
.  PS: My phone will often cause speaker noise when it is not in use. I've always assumed that this was happening when the phone checked in with the towers.
donjoy (author)  NachoMahma6 years ago
Ok fine Thank you !!!!
NachoMahma6 years ago
. Try Googling your topic's title. The generic name for what you are looking for is an RF signal detector.
donjoy (author)  NachoMahma6 years ago
Thank you for the answer....I could find some detectors for this. I have few more questions to add up

1. These detectors detect the GSM signal and it alarms when the phone is ON.
I'm looking for something which gives an alarm when the phone is used for communication (Calls or SMS) Is this possible ?

2. Is there a way to find which is the mobile ON or in use?

3. In the scenario which I mentioned, some people are allowed to use the phone. So is there a solution where we can say exclude XXX,YYY,ZZZ. Is this possible?
. I'm no expert, so these are pretty much guesses.
.  1) Maybe you can detect an increase in power when the phone is in use. IIRC, "checking in" only takes a few seconds, if you see an increase in power for more than a few secs, it's probably a call.
.   2) You could triangulate, but that's probably more complicated than what you are looking for. You might be able to ID the phone number by intercepting/interpreting the data stream, but that may be illegal.
.  3) See second part of #2
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