signals for example some will detect from 5 meters away, some from 10 meters and some from 20 meters. The circuit cannot detect voice contents; it will only detect the encoded signal. Cell phones generate these encoded signals when you receive or do calls or send or receive SMS on you cell phone. The circuit can be used for many purposes for example finding a lost cell phone, detecting cell phone in examination halls or where these are not allowed etc.

The circuit is very easy to build, and using very few low cost components. The heart of the circuit is a lm324 quad opamp IC. The IC contains four high gain opamps. But in this circuit we have used only one of them. At the output of the IC a 2N4401 transistor is connected to drive the LED and a peizo buzzer. You can also remove the LED or peizo buzzer as desired. The Number of LEDs can also be increased. The number of LEDs should not be increased from 25. The operating voltage of the circuit is 4.5V to 12V DC. If you are operating the circuit with lower voltage than 9V then change the current limiting resistor value of the LED from 470 ohms to 220 ohms in all LEDs you are using. The sensitivity of the circuit can be adjusted with 100K variable resistor.


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The figure shows a very easy project of a cell phone detector circuit. The circuit is quite sensitive and can detect a cell phone from 10 to 20 meters away. The detection range also depends on the type of cell phone you are using, because all cell phone generates different strength
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Easy Cell Phone Detector Using LM324 IC