This is a project of a very sensitive mobile phone detector circuit using a CA3140 opamp IC, a 555 timer IC and few other discrete components. The circuit is able to detect a mobile phone / cell phone from 8 to 10 meters away or more, you will find different range with different brands cell phones.
The circuit is using two ICs, the IC1 is working as a signal amplifier and IC2 is working as a time delay. When any cell phone signal will be received the 555 timer IC will become triggered and activate an LED and a peizo buzzer for few seconds.
The circuit can be used for many purposes, it can be used at the places where cell phone are not allowed for example at examination halls. It can also be used to find a lost cell phone even if the phone is set on vibration alert or on low volume ringtone. The operating voltage of the circuit is 6V to 12V DC. You can also use any small size batteries with the circuit.