Cell Phone Detector circuit


BySaddam 43

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.


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  • Alois Baltazar's picture
    Alois Baltazar
    Nov 30, 2016

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

  • Mushfick's picture
    Mar 06, 2018

    Use a 2m long copper wire..

  • Garvit Karagwal's picture
    Garvit Karagwal
    Aug 31, 2018

    How Much Distance Does It Covers ?

  • Gil Ribeiro's picture
    Gil Ribeiro
    Dec 02, 2016

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

  • hasnain's picture
    Dec 11, 2016

    sir how to specify anteena

  • sravani 's picture
    Dec 19, 2016

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

  • Abhishek's picture
    Dec 31, 2016

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

  • Arun's picture
    Dec 21, 2016

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

  • Dunes 's picture
    Dec 23, 2016

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

  • Anmol's picture
    Jan 17, 2017

    I want to know about basic principle of the circuit.

  • swapandeep kaur's picture
    swapandeep kaur
    Feb 03, 2017

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

  • biruk satnaw's picture
    biruk satnaw
    Mar 18, 2017

    can you explain the working principle of the circuit?

  • Devendra's picture
    Apr 01, 2017

    Is this device compatible with 3g frequency of mobiles

  • Moumon Bhar's picture
    Moumon Bhar
    Apr 04, 2017

    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.

  • Gana's picture
    Apr 18, 2017

    Howzit man,

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

  • hamlin's picture
    May 09, 2017

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

  • OLLO PAULINUS's picture
    May 23, 2017

    please how do i increase its range?

  • Kiran's picture
    Jun 14, 2017

    It's very good article but written material is less

  • adi's picture
    Jun 20, 2017

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

  • Bansuk lyngkhoi's picture
    Bansuk lyngkhoi
    Jul 23, 2017

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

  • janet's picture
    Jul 28, 2017

    pls i need the complete material for this project topic

  • Darshana's picture
    Jul 29, 2017

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

  • Darshana's picture
    Jul 29, 2017

    My circuit is glowing without any cell phone ringing

  • JeanneFRIES's picture
    Aug 06, 2017

    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.

  • Naveen's picture
    Oct 11, 2017

    Can u send the block diagram of detector without using antenna

  • ken's picture
    Oct 20, 2017

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

  • Saurabh's picture
    Oct 22, 2017

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

  • Naga pandi's picture
    Naga pandi
    Oct 28, 2017

    Nice therory explain

  • jose's picture
    Nov 15, 2017

    Do you have a working proteus simulation?

  • Icha's picture
    Nov 22, 2017

    What kind of antenna is this ?

  • ahmad's picture
    Dec 06, 2017

    plzzz tell me about loop antenna

  • Jack 's picture
    Jan 29, 2018

    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

  • AISHA's picture
    Jan 30, 2018

    The full project is already explained in this website

  • Jackson's picture
    Apr 04, 2018

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

  • Abhishek's picture
    Apr 14, 2018

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

  • Mounika's picture
    May 11, 2018

    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

  • berihun ashagrie's picture
    berihun ashagrie
    May 31, 2018

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

  • Arijit Roy's picture
    Arijit Roy
    Jul 13, 2019

    sir,i make this circuit but it does not working hence i use 24pf in C6 and C7 instead of using 22pf,i can't understand how it does not works so please tell me the reason as soon as possible,thank you

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