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Electronic Eavesdropping Devices Detector


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  • 7 months later...

I am a new electronics hobbyist, and I am very interested in this circuit for use in a current investigation (can't elaborate much). Anyway, I am looking for a schematic like this that will detect up to 3000MHz. Therefore, my question would be: How do I modify this schematic to detect up to 3000MHz? I pretty new to any kind of RF electronics (building). Thanks for the help.

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Hi Sarge,
Welcome to our forum.
You are talking about detecting very high frequency microwave frequencies, where a short piece of wire is a tuned circuit and a short piece of metal is an inductor. Therefore a special wiring technique must be used (waveguides) that resembles plumbing.
Also, parts that operate at high microwave frequencies are not readily available.

This simple circuit is not tuned and would be overloaded by every radio and TV station, taxicab radios and anything else that transmits nearby.
Good luck.

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Hello there,

Just like sargehendricks I'm quite new to this stuff. (cannot elaborate on the purpose of constructing the gadget either...) I created this device from scratch, simply bought the components, blank circuit board and not to forget soldering iron from the local store. It now seems to work, so I'm quite proud... 8)

Question: I tried it before puting it in the metal box. Adjusted the pot-meter so that the sound was barely there. As soon as I start to move the antenna the sound goes crazy. Is this because it's not in the metal case or does this mean my entire appartment is bugged ;D? I tried to 'detect' the signal from my cell-phone, but when I move the phone (while calling some number) towards the antenna, the sound from the speaker becomes less... ???

Can anyone help me out??

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I am intersted in your rf sniffer project. several questions

1 would you be able to make it tunable so that you can select a required frequency.

2 Does the sniffer pick up normal am reciver signals

3 could you incorporate a data slicer at the output stage so data could be fed into a PC

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Hi Jason,
Welcome to our forum.
The project is just a simple circuit that detects a transmitter by making a tone. When you touch its antenna then you also become its antenna and it picks up more radio and TV stations, taxi cab radios etc.

When you move your transmitting cell-phone closer to it, the pitch of the tone should increase, unless you have its sensitivity control set too high and it is overloaded.

Hi Maximus,
Welcome to our forum.
1) You could tune it by replacing its R7 with a high-Q parallel LC network.
2) It picks up any RF within its frequency range and sensitivity. If you added tuning and it received a radio station, you wouldn't hear the program, just a tone.
3) Its output stage just provides a tone, no data.

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Hello Audioguru,

Thanks so far for the help. I have almost completed the construction of the gadget. Now that the circuit board is in the metal box, I don't have the problem I had before, that the thing reacted to every movement. I can now adjust the pot-meter so the tone is reduced to a mere cracking sound. However when I move my cell phone towards the antenna the pitch does not change at all. Do you have any idea what could be wrong. I fear that if a potent transmitter such as a cell phone is not detected, it will be an illusion to sniff out the real bugs.

Do I understand it correctly that the ground (-) of the circuit should be connected to the metal casing??

I attached a pic of what it looks like so far...

Hopefully you can help me out before I close the case.

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Hi Jason,
Maybe the VCO isn't working properly and doesn't change the pitch of the tone with changes in signal strength.
Maybe your cell phone operates at a radio frequency higher than this project can detect.
Try driving it closer and closer to a radio or TV transmitter with its sensitivity turned way down, to see (hear?) if it works.

It is good that your metal box made it more stable. You are correct, the circuit's ground (-) connects to the box.

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  • 4 weeks later...


I do like this little gadget.

I did read the previous postings and was wondering [based upon the requests of other] whether it would be possble to publish a RF sniffer that can detect a TV.

I am asking because I run a website to abolish the TV Licence in the UK.

The company who collects the TV Licence fee claims it has sophisticated TV detection equipment ... but it would be cool to show people it is a simple device that anyone can build :-)


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Hi Erik,
Welcome to our forum.
Are you guys in the UK charged a fee to turn-on or just to own a TV?
That's outrageous! What's the fee for, don't you guys have commercials? Or is it just to pay for their "sophisticated TV detection equipment"? Sounds like a make-work project for the unemployed.

Here in Canada I've heard that cable TV companies have "sniffer trucks" with high-gain, very directional antennae to discover us techies who descramble their pay-per-view. They actually demo'd a truck to scare us. We noticed that its antenna was mounted backwards and the cable to it was a garden hose!
Gimme a break! I doubt that even NASA could detect my TV's local oscillator in the next room. Besides, cable here is all-digital now so most people just steal neighbouring USA's satellite TV.

I think that this little gadget would be overloaded most of the time by local radio and TV stations, since it isn't tuned.

Good luck getting rid of that crazy licence.

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  • 2 weeks later...

Hi Badai,
I just finished replying to your other posts about this project!
Please keep all your questions in this thread.

You can't use a breadboard for high frequencies because the capacitance between its tracks is 20 times or more than on a PCB, and the inductance is also much higher.

Of course you can use a single wire for an antenna, the project spec'd using a telescopic antenna which is like a piece of wire.

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actually i'm a beginner user for EAGLE Layout Editor, so I'm not sure either i draw the layout right or not. Can you send me the pcb design(electronic eavesdropping devices detector), so i can send directly the transparent directly to pcb lab at my faculty?

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  • 1 month later...

Hi everybody, I'm new to this forum.

I built the rf sniffer circuit only to find that it didnt work - the schematic doesnt match the actual PCB layout at all. Take a second glance! When I built the circuit according to the PCB layout, including enclosing it in a metal box, I found that it was just sounding continuously... It only responded to my cellphone while I was making a call, and when it was held within inches from the device. Any clues as to what problems I may have encountered?

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Hi Duke,
Welcome to our forum.
I am sorry to hear that the project didn't work for you.
Please tell us what errors you found on its pcb layout.
1) Did you substitute any parts?
2) When you turn down the sensistivity control, dose the pitch of the VCO reduce to a low-pitch growl or stop?
3) Do you have a strong radio or TV transmitter nearby ?

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