Cell Phone Detector Circuit

Cell Phone Detector is a circuit that can sense the presence of any activated cell-phone nearby and gives an indication of activated cell-phone near around of it. Basically Cell-phone detector is a Frequency Detector or a Current to Voltage Converter Circuit which catches frequencies about 0.8 - 3.0GHz (Mobile band frequencies). RL tuned circuit (Resistor–Inductor circuit) is not suitable for detecting the RF signals in GigaHertz range.

This Mobile Detector Circuit can detect incoming/outgoing calls, messaging, video transmission and any SMS or GPRS uses within the range of 1 meter. This circuit is very useful to detect Cell-phones at Cell-phone restricted places like Exam halls, meeting rooms, hospitals etc. It is also useful in detecting the unauthorised use or spying using hidden Cell Phone. It can detect the RF Transmission from the Mobile Phone and triggers Buzzer to produce beep sound, even if the phone is kept on Silent mode and this alarm continues beeping till the presence of RF signals.


Required Components:

  • Op-Amp CA3130
  • 2.2M resistor (2)
  • 100K resistor (1)
  • 1K resistor (3)
  • 100nF capacitor (4)
  • 22pF capacitor (2)
  • 100uF capacitor         
  • Bread board
  • 9 Volt Battery
  • Battery Connector
  • LED
  • Transistor BC547
  • Transistor BC557
  • Connecting wires
  • Buzzer
  • Antenna


Circuit Explanation:

In this circuit we have used a CA3130 OP-Amp IC for detecting incoming or outgoing signal around it.  Op-amp non-inverting end is connected to Vcc through 2.2M resistor and it is also connected to the ground through 100K resistor and 100uF Capacitor. Its inverting terminal is feedback from its output through a 2.2M resistor for amplify the signal. Two 100nF capacitors are connected between inverting and non-inverting terminal, working as loop antenna for the system. Two 100nF capacitors are connected in series between Pin 1 and 8 of op-amp to boost the gain of the current to voltage converter at its output pin.

Output of this op-amp is connected at the base of NPN transistor namely BC547 through a 1k resistor and a LED is connected at its emitter for indication. A buzzer is also used for sound indication by using a PNP transistor namely BC557. And a 9 volt battery is used for powering the circuit. Rests of connections are shown in the Circuit Diagram below.



Working Explanation:

This circuit consist an op-amp with some active passive components. A LED and buzzer are used for indication of presence of cellphone. Op-amp is configured as Frequency Detector or Current to Voltage Converter and its output is connected to a LED and buzzer using NPN and PNP transistors.


Working of Mobile Detector is simple. Two 100nF capacitors (C2 and C3), in parallel, are used for detecting RF signal from Mobile Phone. These capacitors are working as loop antenna for the system. When there is any call or SMS then capacitors in parallel detect the data transmission frequencies or RF signal and output of op-amp goes high or low (fluctuating) due to generated current at the input side of op-amp. Due to these fluctuations, LED turns on and off through NPN transistor according to the signal’s frequency. Now PNP transistor is also triggered with the same frequency and buzzer starts beeping until data transmission gets finished. If you are not familiar with working of Op-amps then learn more about Op-amps here.


Comments (38)

  • Alois Baltazar's picture
    Alois Baltazar

    Hi, can I ask what type of antenna does this use? And where can I buy it? Thanks!!!

    Nov 30, 2016
  • Mushfick's picture

    Use a 2m long copper wire..

    Mar 06, 2018
  • Gil Ribeiro's picture
    Gil Ribeiro

    Hi, Thanks for this article! But I am curious about the antenna too. How to specify the correct antenna for this circuit?

    Dec 02, 2016
  • hasnain's picture

    sir how to specify anteena

    Dec 11, 2016
  • sravani 's picture

    can u please tell me?which type of antenna used for this circuit?Is it gives indication of other mobiles which is located nearby?

    Dec 19, 2016
  • Abhishek's picture

    Two 100nF capacitors have formed the loop antenna, no other antennas are used. Learn about loop antennas.

    Dec 31, 2016
  • Arun's picture

    is the output is verified.. and also can i use 100 uf capacitor instead of 100nf capacitor

    Dec 21, 2016
  • Dunes 's picture

    Please responce me>>How loop antenaa cap C2, C3 value is decided with respect of radio freq.

    Dec 23, 2016
  • Anmol's picture

    I want to know about basic principle of the circuit.

    Jan 17, 2017
  • swapandeep kaur's picture
    swapandeep kaur

    please explain complete working of complete circuit with significance of each and every component

    Feb 03, 2017
  • biruk satnaw's picture
    biruk satnaw

    can you explain the working principle of the circuit?

    Mar 18, 2017
  • Devendra's picture

    Is this device compatible with 3g frequency of mobiles

    Apr 01, 2017
  • Moumon Bhar's picture
    Moumon Bhar

    I want to know how the Rf frequency of the signal is transformed into current in the circuit. That is for different frequencies I want to measure different current flowing in the circuit.

    Apr 04, 2017
  • Gana's picture

    Howzit man,

    After C7, that coiled-upped connector, is that what you used for your antenna?

    Apr 18, 2017
  • hamlin's picture

    Sir,can u please say what type of antenna to use.

    May 09, 2017
  • Abhishek's picture

    A simple Jumper wire is used as Antenna.

    Jul 12, 2017
  • OLLO PAULINUS's picture

    please how do i increase its range?

    May 23, 2017
  • Kiran's picture

    It's very good article but written material is less

    Jun 14, 2017
  • adi's picture

    this is a very good material this circuit works thanks so much

    Jun 20, 2017
  • Bansuk lyngkhoi's picture
    Bansuk lyngkhoi

    Can you explain more about the working principle the circuit and which antenna do we used

    Jul 23, 2017
  • janet's picture

    pls i need the complete material for this project topic

    Jul 28, 2017
  • Darshana's picture

    Hey I made the circuit, but it's glowing without any detection of a mobile! What do i do?

    Jul 29, 2017
  • Darshana's picture

    My circuit is glowing without any cell phone ringing

    Jul 29, 2017
  • JeanneFRIES's picture

    mine is as well - are there other videos of this project? perhaps something is connected incorrectly? It also looked like the schematics vary slightly from what is pictured in the video, but hard to tell.

    Aug 06, 2017
  • Naveen's picture

    Can u send the block diagram of detector without using antenna

    Oct 11, 2017
  • ken's picture

    Good day! What is the schematic diagram of this cellphone detector ? Can you please help me how to build it? Thank you

    Oct 20, 2017
  • Saurabh's picture

    Sir can you please send me or tell me what is the procedure of antenna , how it is detecting ?

    Oct 22, 2017
  • Naga pandi's picture
    Naga pandi

    Nice therory explain

    Oct 28, 2017
  • jose's picture

    Do you have a working proteus simulation?

    Nov 15, 2017
  • Icha's picture

    What kind of antenna is this ?

    Nov 22, 2017
  • ahmad's picture

    plzzz tell me about loop antenna

    Dec 06, 2017
  • Jack 's picture

    Good day sir.! I acknowledged your work and how you are helping the youth by impacting on them.

    Please sir can you help me with the full material of the project (cell phone detector) and circuit diagram
    Thanks and remain blessed

    Jan 29, 2018
  • AISHA's picture

    The full project is already explained in this website

    Jan 30, 2018
  • Jackson's picture

    Please can you send me the materials and the circuit diagram. Thanks alot

    Apr 04, 2018
  • Abhishek's picture

    Sir ,i riguped the ckt ...by connecting battery it starts beeping sound and also led starts glow.
    Wt is the reason for this??!

    Apr 14, 2018
  • Mounika's picture

    Does it work only when the phone is used for calling? Then how to identify the phone when it is idle or doing other activities other than calling

    May 11, 2018
  • berihun ashagrie's picture
    berihun ashagrie

    Please responce me>>How loop antenaa cap C2, C3 value is decided

    May 31, 2018

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