Mobile Phone Detector Using LM358

By Kumar Abhisekh


This mobile phone detector can sense the presence of an activated mobile phone from a distance of four to five metres. So it can come handy in an examination hall or meetings where mobile phones are not permitted.

The circuit can detect incoming and outgoing calls, SMSes, Internet and video transmissions even if a mobile phone is kept in silent mode. When it detects an RF signal from an activated mobile phone, its LED starts blinking and continues to blink until the signal stops. The author’s prototype is shown in Fig. 1.

mobile phone detector prototype
Fig. 1: Author’s prototype (a) when a call is not detected and (b) when a call is detected

Circuit and working

Circuit diagram of the mobile phone detector using LM358 is shown in Fig. 2. It is built around LM358 (IC1) and npn transistor BC548 (T1).

Circuit diagram of the mobile phone detector
Fig. 2: Circuit diagram of the mobile phone detector

When a mobile phone is active, it radiates RF signal that passes through nearby space. The signal contains electromagnetic RF radiation from the phone.

Capacitor C1 is used in the circuit to detect the RF signal from the mobile phone. When the mobile phone radiates energy in the form of RF signal, C1 absorbs it and passes on to the inputs of IC1. This is indicated by the flashing of LED1. Preset VR1 (2.2M) is used to vary the range of the circuit. Transistor T1 is used to amplify the signal obtained at pin 1 of IC1.
The circuit is applicable for 2G networks, GPRS and network search (manual/automatic). It does not detect 3G, WCDMA and HSDPA network signals so well.

Construction and testing

A single-side PCB layout for the mobile phone detector circuit is shown in Fig. 3 and its component layout in Fig. 4. After assembling the circuit on the PCB, enclose it in a suitable plastic box.

Actual-size PCB layout for the mobile phone detector circuit
Fig. 3: Actual-size PCB layout for the mobile phone detector circuit
Component layout of the PCB
Fig. 4: Component layout of the PCB

Download PCB and component layout PDFs: click here

The circuit works off a 4.5V DC power supply.

Kumar Abhisekh is an electronics hobbyist

For reading other exciting DIY projects: Click Here

This article was first published on 28 March 2017 and was recently updated on 27 December 2018.



  2. Sir, plss tell me what if in case the mobile phone is neither receiving message or calls nor the data is turned on..In this scenario the person is using the phone but it won’t be detected by our detector..Is there any other circuit which will sense the mobile network..Nd also something which will sense the presence of a mobile phone which is on flight mode?

    • The circuit will not detect your mobile phone if it is not activated in normal mode or working mode. It will not detect in flight mode because this circuit can detect mobile phone only through its incoming and outgoing signals.

  3. Why it does not work well for 3G whereas 3G is also an RF signal like 2G ? And modifications in it can make it work for 3G also…?

    • 4.5V power supply is required in the circuit, it can be AC/DC adaptor having 4.5V output, it can be three 1.5V battery cell or it can be a single 4.5V lead acid battery. You can also try with 9V battery, it will work but in that case a slight changes may be required in the circuit.

  4. Sir,My own circuit from your made have turn on with just plug in the battery (9v).On my home have WiFi connection.So what’s wrong with my own??

  5. Hello Sir ,
    I appreciate for you nice concept and I would like to know whether I can use a strip antenna while designing a PCB

  6. Good afternoon, i noticed the parts list calls for (2) 1uF electrolytic capacitors can i use 1 uF ceramic capacitors instead?

  7. hello sir..i appreciated your project and pcb..
    sir i want to work with i m pursiung 4th yr.
    and i interested in this field…so thats why this region i chooses ec branch..and i have knowledge electronics component and already i took training with PCB design and EMBEDDED system.

  8. Do you mind explaining the rest of the circuit. Only C1 and T1 are explained. Does the amplifier convert current to voltage ?

    • does the operational amplifier work as a comparator or current to voltage converter or something else. also can you give the design equations with which you have selected the values for the resistors and capacitors.

  9. Hey.
    I implemented the circuit and it worked but after few minutes the Led remain constantly ON.. Like one of the capacitor is charged already.. How can I make it discharge so to maintain proper work


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