Can Arduino detect a cell phone?

Hi everyone, I am new in the Arduino world, but willing to learn a lot. I am actually working on a project and here is my question: Can the Arduino detect a cell phone? And if yes how, what else do I need to get?

Basically I want to know if it's possible to make the arduino light an Led when a cell phone is in a perimeter of about 5 meters from it. Is it catching the frequency? The electromagnetic field? I would also like that the Arduino make the difference between a cell phone and all other consumer electronics (TV, radio, etc).

Thanks a lot!

Is this an assignment from school or something? Amazing how similar this question is to:

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1210727295

Duncan.

Wow! Pure coincidence. I've read the other post, but did not get everything. So, would it work even if the cell phone is not making calls? If its just turned on?

A cell which is just waiting for a signal from the basestation doesn't transmit much, just a weak keepalive. A cell which is setting up to make a call kicks out a LOT of signal, so is a lot easier to separate from all the other types of communication around the same waveband.