please help me in mobile detector for college

hai peoples.. i am in a emergency of creating a mobile dteector in my college so please send me a clean and well explained circuit for the mobile detector.
it should proud some kind of visual or audio response when it detects the mobile..
is it possible to detect if the mobile is in off condition,
thanks allot if you help t

hai arunmag

This is a mobile phone sniffer circuit that can detect the signals being used in the GSM (Global System for Mobile Communication) band at about 900 MHz. Since the signals are digitally encoded, it can detect only the signal activity, not the speech or the message contents. A headphone is used to hear the detected signals.
here are two separate detector units. Every detector unit consists of a dipole antenna, a choke and a diode. The antenna receives the GSM signals in media. Then a small amount of charge is induced in the choke. The diode demodulates the signal and finishes detecting. The diodes must be schottky diodes or germanium diodes. Since the forward voltage of a silisium diode is high, it won't give a sufficient result in this circuit.
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