Cell Phone Detector aka Mobile Bug

This handy mobile bug or cell phone detector, pocket-size mobile transmission detector or sniffer can sense the presence of an activated mobile cellphone from a distance of one and-a-half metres. So it can be used to prevent use of mobile phones in examination halls, confidential rooms, etc. It is also useful for detecting the use of mobile phone for spying and unauthorised video transmission.

The circuit can detect both the incoming and outgoing calls, SMS and video transmission even if the mobile phone is kept in the silent mode. The moment the bug detects RF transmission signal from an activated mobile phone, it starts sounding a beep alarm and the LED blinks. The alarm continues until the signal transmission ceases.

Cell Phone Detector Circuit Schematic

mobile bug cellphone detector

An ordinary RF detector using tuned LC circuits is not suitable for detecting signals in the GHz frequency band used in mobile phones. The transmission frequency of mobile phones ranges from 0.9 to 3 GHz with a wavelength of 3.3 to 10 cm. So a circuit detecting gigahertz signals is required for a mobile bug.

Here the circuit uses a 0.22μF disk capacitor (C3) to capture the RF signals from the mobile phone. The lead length of the capacitor is fixed as 18 mm with a spacing of 8 mm between the leads to get the desired frequency. The disk capacitor along with the leads acts as a small gigahertz loop antenna to collect the RF signals from the mobile phone.

and another video from Sufyan Ghori

Op-amp IC CA3130 (IC1) is used in the circuit as a current-to-voltage converter with capacitor C3 connected between its inverting and non-inverting inputs. It is a CMOS version using gate-protected p-channel MOSFET transistors in the input to provide very high input impedance, very low input current and very high speed of performance. The output CMOS transistor is capable of swinging the output voltage to within 10 mV of either supply voltage terminal.

Capacitor C3 in conjunction with the lead inductance acts as a transmission line that intercepts the signals from the mobile phone. This capacitor creates a field, stores energy and transfers the stored energy in the form of minute current to the inputs of IC1. This will upset the balanced input of IC1 and convert the current into the corresponding output voltage.

Capacitor C4 along with high-value resistor R1 keeps the non-inverting input stable for easy swing of the output to high state. Resistor R2 provides the discharge path for capacitor C4. Feedback resistor R3 makes the inverting input high when the output becomes high. Capacitor C5 (47pF) is connected across ‘strobe’ (pin 8) and ‘null’ inputs (pin 1) of IC1 for phase compensation and gain control to optimise the frequency response.

When the cell phone detector signal is detected by C3, the output of IC1 becomes high and low alternately according to the frequency of the signal as indicated by LED1. This triggers monostable timer IC2 through capacitor C7. Capacitor C6 maintains the base bias of transistor T1 for fast switching action. The low-value timing components R6 and C9 produce very short time delay to avoid audio nuisance.

Assemble the cell phone detector circuit on a general purpose PCB as compact as possible and enclose in a small box like junk mobile case. As mentioned earlier, capacitor C3 should have a lead length of 18 mm with lead spacing of 8 mm. Carefully solder the capacitor in standing position with equal spacing of the leads. The response can be optimised by trimming the lead length of C3 for the desired frequency. You may use a short telescopic type antenna.
Use the miniature 12V battery of a remote control and a small buzzer to make the gadget pocket-size. The unit will give the warning indication if someone uses mobile phone within a radius of 1.5 meters.


Join the conversation!

Error! Please fill all fields.
  • durgha dhevi

    i tried this circuit but it didnt work so please send me a suggestion pls .many people posted that they got output so pls help me send me your suggestions

  • Mohan

    Is there any one in Chennai to do this project.i am not from ece so i want some one’s guidance.

  • durgha dhevi

    i tried the above circuit .my cicuit is working even when i remove the antenna .but when rps is switched of led stops glowing i cnt find the reason for failure i want to submit my project in one week please give me some suggestios so that i can get my project succeeeded.

  • manoj yajamanam

    You can also use this circuit with 9v battery and capacitor c5 of 47p is not required to be connected.!

  • jigar mehta

    I am Third year(T.E) engineering student studying in electronics and telecommunication branch from the university of Mumbai.
    i am working on the cell phone detector circuit. After mounting the circuit on breadboard , the buzzer rings and LED is glowing even when the mobiles are switched off .
    I need a solution to rectify this problem at the earliest as my date of finalizing the project is approaching. Please contact me as soon as possible. My contact details are as follows:
    Contact number:1) +91-9699969951
    Thanking you,

    warm regards,
    (Jigar B. Mehta)

  • daniel

    how can i get the 12 v battery

  • Kishan


    I am looking for a guy in Hyderabad who can make this for with little modification

    please contact me at my email id

    Many Thanks in Advance!!

  • daniel

    sir,will you please tell me all design equations and working of each part,mainly use of capacitor after the antenna and working of ca3130.
    please send me mail on

  • rayan

    please Mr i need your help
    i have find ca3140 instead of ca3130 is it the same ?
    in the datasheet nothing will differ
    but i builded my project and it doesnt work and i dont know why?
    a need a quick answer plz
    thnk u

    • Ritam

      ca3130 is an op-amp. all op-amps does the same thing but their operating frequency ranges are different. i tried this project and it worked for me. i was facing the same problem when i did it the first tym. check if all connections are correct or not and whether all components that should be grounded are properly grounded.

    • Inder

      hi Ravan, Use ca3130 only. Circuit won’t work without it.

  • Inder