Cell Phone Detection

Hello, I am new to this forum. My senior project group is currently working on a cell phone detection system that would detect the presence of a cell phone around 1-2 meters away. So far we have tried detecting EMI but we found it to be extremely difficult because phones today are extremely well shielded thus making small signals very difficult to detect.

Another thing we tried is RF pulse detection where we are sending a modulated square wave from one antenna to another and detecting changes in the signal (amplitude and time delay) when a phone is present in the field. I confirmed that metal detection might work for this project but I'm not sure how to reduce false alarms such as a person's keys or jewelry. However, we would like to pursue a more intuitive approach to this problem. We confirmed that we could pick up transmitted signals while the phone is in use and when it's in idle mode searching for a tower.

I'm wondering if you have any ideas on how we could detect the presence of a cell phone. What kinds of signals do cell phones transmit that we can detect? So far I know that modern smart phones could receive several different signals such as WiFi, GPS, and Bluetooth. Our objective is to make a device that would detect the presence of cell phones and we've thought of system integration where we put multiple sensors in a system that would help each other detect a mobile phone.

Signal strength meter on the TX frequencies would be a good place to start

Believe it or not if you use google and do a quick search by typing in the keywords you are looking for + schematic The diagram is actually on the net at address

http://electroschematics.com/wp-content/uploads/2009/01/cellphone-detector.jpg

So far, we were successful in detecting a transmitted signal when a phone call or text message is being made; we saw it on a spectrum analyzer. However, we are trying to detect a phone while it's in idle mode, when the phone is powered on, but not in use. I know that cell phones are continually trying to communicate with the nearest tower and when there's poor reception, I notice that the cell phone's batteries drains faster. This is an indication that it's using more power to communicate with the tower. Similarly, when the phone is in an area with good reception, it doesn't drain the batteries that much. *Is there a way to detect these signals?*

I'm trying to use an RMS power detector that would input an RF signal and output a DC signal that would connect to an LED bar meter. I'm thinking of adding a couple filters so that it could detect on certain frequency bands (e.g. 800 MHz & 1900 MHz).

I also know that modern (smart) phones nowadays have WiFi, Bluetooth, and GPS, but it's up to the user to turn on those signals or not. *Are there any other signals from a cell phone that could possibly be detected?*

The answer to this is no unless of course you can detect the oscillations radiated by the CPU or perhaps the LCD other than this The cell phone going back to the days of ETACS which of course has now changed

Cell phones works on channel hopping and control channels now of course digitised and a continuous bit stream

In theory if you new what commands were being sent out by the cell site you could mimic these and then proceed to interrogate the cell phone but of course this would require that you know the serial number or the ESN of the mobile or alternatively the Mac address or IP address That would mean you would need to know what phone you are paging

You require that you are able to detect a cell phones presence I’m not sure what the time period is now between burst’s to let the cell site know what area the cell phone is in

There is of course Bluetooth as well but again this means that the cell phone would have to be in TX mode to identify the phone as being present

However this boils down to the same old story and this is listen in on the control channels of the site which is a perpetual stream and then possibly identify what phones are in the area covered by that site This also may well be encoded I.E data not readily decipherable from the Joe publics point of view

Other than this theoretically there is no way to detect a cell phones presence other than the periodic burst of transmission ever 20 / 30 minutes What the current system is now again I don’t know maybe a search on the net might reveal this

Ther are a few questions to ask.
First are you looking at a specific type of phone? 3G 4G 4GLte 5G GSM CDMA...
Second are you looking at a specfic carrier? Sprint AT&T TMobile Cricket Boost....
Third are you looking at a specfic manufacturer? Apple Samsung LG Nokia....
Fourth are you looking at ONE phone?

Do you want to monitor across all channels or just poll channels
Do you want active voice?
Do you want active data?
Do you want active SMS?
There are 64,535 possible activities to monitor for (determined by carrier.and FCc)
And the current US Broadband spectrum runs in blocks from 800mhz through 5ghz.
And is split clockwise for A carrier and counterclockwise for B carrier in each Cell.

If you're looking for a SIMPLE detector I recommend you pick a single pollling frequency, then build a simple "_LC OP-Amp comparator circuit_" that comes within rang of your loop.