A anti-spy or bug detector circuit is a device that detects hidden wireless electronic devices such as wireless microphones, spy cameras, Wi-Fi devices, GPS trackers or any gadget that emits some kind of radio frequency (RF).
The proposed design can be specifically used as:
- Wi-Fi Signal Detector Circuit
- FM Transmitter Signal Detector Circuit
- Wi-Fi Spy Camera Detector Circuit
- Wireless Mic Detector Circuit
Contents
Overview
Also called anti spy RF sniffer, these are usually used to scan and detect hidden electronic surveillance, that may be installed to secretly monitor a "target" or an opponent and secretly learn about their plans.
Bug devices are mostly used by detective agents, police, and secret agents for tracking the behavior of a suspected criminal, or a personal client.
The bug detector circuit presented here is exclusively developed by me, and can be used for detecting, pinpointing any hidden wireless device or unwanted surveillance planted in a room.
The hidden spy devices could be inside beds, cupboards, tables/chairs, flower pots, or in fact anywhere a normal individual would least suspect.
Identifying such hidden unwanted surveillance system can be impossible without using costly and sophisticated equipment. However, the circuit idea presented here is not only cheap to build, it also accomplishes the job with utmost perfection.
The complete circuit diagram can be seen below:
Video Test Result
NOTE: the sensitivity of the circuit can be adjusted to much higher levels either by increasing the 2M2 resistor value, or by adding two more op amp stages in series with the above design, since we already have two extra op amps in spare inside the IC.
Pictorial Presentation
Circuit Description
The circuit is basically built using the quad op amp IC LM324. Although the IC has 4 op amps in-built, only two op amps are actually implemented for the bug detector application.
The A1 and A2 stage are identical and both are configured as high gain inverting amplifier circuits.
Since the two amplifiers are joined in series the total gain is highly enhanced making the circuit highly sensitive to RF interference.
Basically the amplifiers work through the following steps:
- The antenna picks up the electrical the disturbances, sends it to the op amp amplifier A1, which amplifies it 10 to 100 times depending on the value of the feedback resistor R1.
- The output from A1 is sent to the next op amp A2 via C2, which blocks the DC ad allows only the picked AC frequency.
- A2 further amplifies the frequency 10 to 100 times depending on the resistor R4. C1 ensures stability to the op amp and avoids stray pick ups.
- R2, R3 ensures the op amp inputs act like differential inputs for detecting minute changes in the received electrical signals.
The circuit is so sensitive that it is easily able to detect all types of electrical noises even thunder lightning interference.
I was surprised when I saw this bug detector circuit easily picking up signals from my wireless Wi-Fi device from a distance of 2 feet. Actually, while the unit was placed on the bed, I found the LED blinking abnormally as if the circuit was unstable and malfunctioning. I was quite disappointed.
Then I picked it up and put it some distance away from the bed, and the LED just shut off. I tried placing it again on the bed and the LED started blinking again. I still couldn't figure out the reason, and thought may be the bed was acting like a large antenna and causing the disturbance.
However, finally I realized that this was happening because my internet WiFi unit was also placed on the same bed at some distance away.
I removed the WiFi device from the bed and the bug detector LED was simply shut off again.
Next, I did a number of repeat tests and was convinced that the unit was actually detecting RF, and the LED blinking wasn't due to an unstable or malfunctioning condition.
Once confirmed I built the final bug detector circuit and presented it here for your reading pleasure!
Parts List
- R1, R4 = 2.2 Meg
- R2, R3 = 100 K,
- R5 = 1 K
- C1, C2 = 0.1 uF PPC
- A1, A2 = 1/2 LM324 op amp
LM324 pinout details can be found below:
RF Sniffer Circuit
The circuit diagram for the RF sniffer can be witnessed in the following figure. RF signals heading at ANT1 are connected through C5 towards the detector circuit stage.
A high impedance ground network intended for wide band detection is supplied by R3. Having inductor L1 hooked up to the circuit by means of S2, the circuit gets adjusted for the FM band. Diodes D1 and D2 perform the job of detection and demodulation. The detected RF signal is transferred to the non-inverting input of op amp IC1 .
The IC1 op amp is constructed like a non-inverting amplifier through a preset gain of approximately 450. The circuit works by using junction field effect transistors (JFETs) at the input sections; which boosts sensitivity because of their high impedance. Potentiometer R9 works like a squelch control which tunes the IC1 offset settings. The amplified detector output which shows up on pin 6 of IC1 is transferred to J1.
An appropriate high impedance phone could be attached to J1 whenever you would like to hear the detected signal. Furthermore, R6 and C6 do the job of cleaning the signal. The cleaned up signal is subsequently given to the input of IC2, which is an LM3914 dot /bar display chip.
The LM3914 or LM3915 device includes a network of resistor and a range of comparators. With respect to the input voltage fed to pin 5, several LEDs will probably light up to show the relative voltage levels. In this RF sniffer circuit, a 9 LED bar display is set up by attaching pin 3 of the IC2 with the positive supply voltage.
When the detected signal is the weakest, this might illuminate only the LED#9. As the detected signal voltage becomes stronger, each of the LEDs in the bar graph turns on one by one until, with the most powerful RF signal level, you might find all the nine LEDs being illuminated.
Resistors R7 and R8 are used to fix the reference voltage for a full-scale bar graph LED display. Observe that we have not used any current-limiting resistors for the LEDs; since the resistors R7 and R8 itself fulfill the function of limiting the LED current.
Parts List
For further inquiries or information please use the comment box below.
NELSON AREVALO C says
THE PROJECTS ARE VERY GOOD, SIMPLE AND FUNCTIONAL, AND CAN BE DONE AT A LOW COST, EXCELLENT FOR WORKING WITH STUDENTS FROM BASIC PRIMARY AND BASIC SECONDARY, THANK YOU.
Swagatam says
Thank you for your kind feedback, much appreciated!
Rokie says
Hello, I made the same circuit with a breadboard. The LED does not show any sensitivity to RF signals, the light does not turn on. I checked my circuit. I couldn’t see any difference. Is there anything in the circuit that is not suitable for doing with a breadboard? I made the connections with jumper cables used in the breadboard. Could these cables act as an extra antenna and cause the circuit not to work, since they make too much length in some places? What could be the problem?
Swagatam says
Hello, there might be some mistake in your circuit connections or the parts. Breadboard is definitely not suitable for this project since a single loose connection can result in the circuit failing to work. You will have to solder the parts over a strip board to make it work.
The circuit has been tested with cellphone also, you can checkout the video in the following article:
https://www.homemade-circuits.com/how-to-make-cell-phone-rf-signal/
NR says
Hello,
Can you answer a question for me please. As a retiree and old school HAM (N7VVC back in the day) I would like to assemble a few things, camera detector, IR detect, sniffer and the like. Not so much for me rather family to use.
My question is, can you suggest a seller of quality kits (complete components and parts)? Just a lot easier to for me at this time to have what I need and put it together.
Thanks. NR
San Diego CA.
Swagatam says
Hello, I am sorry, I do not have any information regarding any seller dealing with these items.
khalid says
Hello sir how are you hope you fine khalid here .sir thankyou very for your help sir i got success in making of 5kva inverter thanks sir. i complete the 5kva inverter and everything is fine frequency i set to 50khz and work fine but i not checked the output because the ferrite core transformer giving some humming sound not very loud very slow but i afraid may be burn so swith off i already put masking tape on outside leg of ecore when i hear sound from tansformer i put masking in middle leg also on ferrite ecore but still have sound so there is no problem with small sound or problem .we can use or it may burn or having any solution for sound please need help sir waiting for reply. And complete report i will give after checking the output and load test so please reply i am waiting for reply thaks.
Swagatam says
Thank you Khalid, but you have posted the question under the wrong article.
Please post this question under the following relevant article:
https://www.homemade-circuits.com/5kva-ferrite-core-inverter-circuit/
I will try to figure it out for you.
Wm says
I have a camera happy landlord who I believe has audio in my home without any power whatsoever through out the Nabor hood and only his generator running at the main house about 75 yards away I still get Rc single stronger than calling out on my iPhone and it seems to run in a line across the wall and I’m not getting anything from my TVs pa speakers or anything magnetic just in spots on the wall and a line running across it too
Should I have Rc without any power to my house at all and like I said it’s more powerful then my cell phone. Help please am I being bugged or just nuts??
Swagatam says
Switch OFF your home power completely and switch OFF all the electronic gadgets in your home and check again for the RF. If it still exists strongly inside your house then probably you are bugged
Dimitrios says
what kind of capacitor you use? the cirtuct can woks with 5v?
Swagatam says
any good quality capacitor will work!
Mike Grupe says
Hi,
My name is Mike Grupe and I am currently studying electrical/electronics engineering at the University of Southern Queensland, Australia. I don’t have much practical electronics experience but after checking out this website – wow!!! Awesome!!! This will enhance my electronics knowledge – a big thank you, my journey in learning electronics just got a little bit easier.
Keep up the good work.
Thanks again,
Mike
Swagatam says
Hi, thanks very much, appreciate your enthusiastic thoughts, and wish you all the best!
Robert M. Swihart says
Sir;
I am interested in eaves dropping detectors. I am a retired Texas Peace Officer, and I head up the security at my church.
First: What antenna configuration or specs are required to recieve a broad range of bands, from cell phones, wifi, GPS on cars, and most things that eaves drop in an office enviroment? In other words, can I build a unit that will use one antenna, and pick up anything in this spectrum?
Second: I would like to be able to “tune” or adjust it, to pick up such signals from about 30 feet away, and set it for a lower sensitivity as I enter the particular room, or closet the bug is broadcasting from. Is this feasible? Maybe a row of LEDs that light up in a range depending on proximity to the bug, or strength of signal.
Respectfully,
Retired L.E.O.
Swagatam says
Hello Mr. Robert, I have one related circuit already posted in this website which is designed for listening to GHz bands, I got this from one of the old electronic magazines. Here’s the link of the article, I hope this does the job for you:
https://www.homemade-circuits.com/listen-to-uhf-and-shf-ghz-bands-with-this-simple-circuit/
Satya says
I need that one too sensitive rf detector for personal use.. can you please tell how much cost charge for making this type of rf detector .if it is possible I want to buy it if you make it for me. Contact personally on my mail.
Swagatam says
If you make it too sensitive, the LED will keep blinking all the time, because RF is present in our home through many different sources, from AC mains lines, from refrigerators, neighboring mobile phone calls, computer, tube lights, fan dimmer etc. Sorry I do not sell this item I can only help the user to build it personally.
Kundana.T says
Can’t we use any other IC ?
Swagatam says
No, LM324 is the recommended iC.
TB14 says
I don’t have a 324 but I have LM3900N. The pinout is different so I’ll need to make sure I have everything in the proper places. Do you think LM3900N will it work as substitute?
Swagatam says
I would recommend LM324 only, which will give guaranteed results, i am sire how other op amps might work.
Kundana.T says
Can you explain me the working of each component in the circuit as I am doing my mini project on this circuit?
Swagatam says
I have updated the explanation in the article….
T.Kundana says
Can you explain the circuit diagram it’s quite confusing
Can I use normal capacitors instead of ppc capacitors
Swagatam says
You can use any good quality capacitor
T.Kundana says
Can you explain circuit diagram connections ?
Swagatam says
You can get more explanation here
https://www.homemade-circuits.com/how-to-make-cell-phone-rf-signal/
shdamaj says
first, I want to thank for this project
second, I couldn’t find a 2.2 M ohm resistor, so I used 3.3 M instead, so the LED won’t blink until it is in direct contact with the signal transmitter, I think I should search for 2.2 M resistor and replace them in order to increase the sensitivity, or what you do say?
Swagatam says
higher resistance value at the feedback will increase the sensitivity of the circuit and may make it unstable…you can use two 1M in series if you are not getting 2M2.
Frank says
Can I use ceramic capacitors or do I absolutely need PP capacitors ??
Swagatam says
PP will work better according to me
Amer says
I want to ask ;is there high and low voltage protective circuits used 324
220vac
Swagatam says
It is there, please use the search box above to find it.
Ale Ian says
Actually I’m having trouble figuring out how to wire any of it together. Could you possibly post a photo of the under side of the pcb to show how you connected all the components together, please? It would be very much appreciated !
Swagatam says
Hi, the soldering side is quite messy so it won’t help much. Instead I have updated it in the pictorial form with all the connection details. you can check it now…I hope it helps!
Ale Ian says
The pictorial is a tremendous help, thank you so much for taking the time to explain the connections!
Swagatam says
Glad it helped, wish you all the best!
John Smith says
Any ideas on how/why it works at all?
From purely theoretical point, it shouldn’t work, because…
1) C1 shorts antenna input to ground in terms of AC (RF input). In case of “ideal” capacitor, 0.1uF would be pretty much negligible impedance for anything that looks like RF.
2) Gain-bandwidth product of LM324 is nowhere close to wi-fi or cellular, it isn’t RF device on its own.
3) There is no obvious explicit RF detector circuit either. So where does RF turns into something LM324 can process, how and why?
As reasonable guess, “real” parts would have plenty of parasitic parameters, say, most 0.1 uF caps would have some “resonance frequency” far lower than cellular or wifi. Past that point they rather behave like inductance instead, due to parasitic inductance of leads/plates overtaking capacitance action. However it isn’t obvious and if one means it have to be inductor, using “explicit” inductance with specified parameters is probably better idea? Then, I can imagine strong RF field can manifest itself by detecting on either ESD protection of inputs, or on input BJT junctions or so, however it nowhere close to being obvious and it would be my best guess I can do, could be incorrect.
p.s. also drawing + and – on opamp inputs in schematics could be good idea. Say I do have LM358 or 2904, at first glance it seems this circuit needs just 2 opamps, these should do as well, unless circuit relies on some extremely unusal parasitic properties of LM324 I’ve failed to foresee. In case of your circuit I have to scroll between IC pinout and diagram to “translate” it into to LM358-based version. Should there be + and – I would rather just redraw circuit by attaching functional pins the way circuit means it – at the end of day I’ve got curious why the hell THIS works at all. So if it actually does, I would definitely bug few “advanced” RF engineers to properly decode how and why it detects anything at all – I bet it can puzzle even seasoned RF engineers 🙂
Swagatam says
Thanks for compelling to investigate this circuit more deeply 🙂
Actually there’s nothing complex about the functioning of the circuit. The op amps are honestly doing what they have been designed to do.
Referring to A1, the non inverting (+) pin3 is tied to ground, and pin2 is also at ground potential via the 100K resistor but is not as grounded as pin3. This makes it highly sensitive to any electrical disturbance even at mV range.
It has nothing to do with the frequency of the RF, it is merely detecting the electrical potential that hitting pin2.
Since the RFs may be fluctuating from across positive and negative cycles, the negative cycle which are more negative than pin3 potential are quickly caught by pin2. causing the output pin1 to go high. This high feedback quickly reaches pin2 back shutting it down, and the cycle is continued causing the LED to flash.
The 0.1uF is actually introduced to blunt of the sensitivity and prevent the circuit from detecting the unwanted disturbances emanating from other possible RF.
I am sorry redrawing the diagram may not be possible because this schematic has been indexed by Google, replacing it may not be good for the article, for the future articles I’ll surely consider adding the +/- to all op amp circuit.
Ale Ian says
Hi- Thanks for sharing this project! I’m new to diy electronics, would you mind sharing how you wired the antenna to the pcb and also how you wired the battery? Thank you!