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
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.
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!
- 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.
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