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Bug Detector Circuit – RF Sniffer Circuit

Bug Detector Circuit – RF Sniffer Circuit

A bug detector 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


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

Simple wireless bug detector circuit

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.

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.

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
  • C1, C2 = 0.1 uF PPC
  • A1, A2 = 1/2 LM324 op amp

LM324 pinout details can be found below:

LM324 pinout details

For further inquiries or information please use the comment box below.


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

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