FM Telephone Circuit

This FM telephone bug is somewhat compact. It is however, on the FM band, so that’s a consideration to make when building it. Wouldn’t it be bad luck if you bugged someone’s phone and they happened to hear themselves talking while their radio was on. Of course, bugging a telephone is illegal in most areas so this is just for the theory of it all.

Here is the list of parts. There are only 11 parts and if you don’t want to use the LED, you wouldn’t have to. On the coil, one thing the author doesn’t mention is that you can buy variable coils. I think that’s sometimes a bit easier than trying to coil some wire up. If however, you feel like coiling wire up, wrap it around a small piece of a pencil. It won’t matter if you leave the pencil stub inside the coil. Buy your parts at Digikey. I recommend them.

(source –

Long Distance Phone Transmitter

I saw this facinating idea where to transmit a phone converstation an unlimited distance another phone was put inline with the first phone’s phoneline. Then when a call is made on the outbound phone, the second phone dials you or someone else and allows the original call to go through.  It’s expensive though, so pretty much out of reach for the common person. I guess though if you could program a cell phone to precall a certain number, that would work though but it would take some programming.!au488

(Disclaimer, this is just for ideas and is likely illegal in many areas. Please check before using these ideas)

Micro FM Transmitter Circuit

This micro FM bug is fairly small. About the size of a small matchbox and it is a neat little project to work on because it uses surface mount componets. Surface mount components are smaller. If you are working on them, buy a good soldering iron. I recommend a Hakko soldering iron. They are great and then you can get a special tip for doing surface mount soldering. Here is a link to the transmitter. It costs about 14 dollars. Alternatively, you can source the parts yourself and then make your own circuit board. I have found that usually takes more time and costs about the same, so I would recommend just buying the project.

Ultra Small 300 Meter Audio Transmitter Circuit

If you are looking to transmit audio transmissions for a good distance but need something small to do it, then this micro spy circuit would be a good one for you.  This very small spy circuit takes very few parts.

560 pf cap
100k reisistor
BA121 Fet (equivilant of NTE133)
22 pf capacitor
Ferrit Core
BF245 (2 of these)
9 volt battery
1nf capacitor
2 100nf capacitors

Please check the laws in your area before using this device.  This device would be great for nature lovers who would like to hear animal sounds outside their house, and with only a few parts, it would be easy to build. (source –

Long Range FM Bug Circuit

Creating a listening device that can transmit conversations or sounds for a longer range can be valuable in surveillance. This FM bug can serve a variety of purposes from listening to sounds, conversations, nature sounds, and other things. Building a listening device is rather easy to do.

First, you will need to purchase the electronic components listed below. There are some instructions referenced here as well. Building a listening device with an FM circuit is a good project to try. The key with the FM circuits that related to their power in transmitting a conversation is the number of transistors in the circuit. There are some strong FM transmitter circuits out there that can transmit for very long distances. There is one 4 transistor pirate radio circuit out there that can transmit for hundreds of miles. This fm transmitter circuit has a pretty good long range. It should, it has 3 transistors. You could have a great FM transmitter if you setup your own radio station and pumped out a couple of thousand watts but that’s not a bug is it. Given the small size of this circuit, it has a good range of up to 2 km.

What are the keys to remember about building an FM listening device or bug.

FM transmitters should be small.
FM transmitters should be easy to build.
FM transmitters should not cost that much to build.

Here are the parts you will need:

2 – 1 47k resistor
1 1u capacitor
1 1n capacitor
1 27k resistor
1 47k resistor
1 1u capacitor
1 1u capacitor
1 1n capacitor
1 6p8 capacitor
1 330 resistor
1 p8 capacitor
1 Inductor made of 6 turns of magnetic wire
1 1u capacitor
1 9 volt battery
1 1n capacitor
1 circuit board or bread board
1 1N914

(source –

FM Telephone Bug Circuit

Creating a telephone bug is not all that difficult. The idea is twofold, you must create a transmitter and you must allow the phone signal to continue. If your transmitter is noisy or has a lot of static, then listeners are going to hear that. So you have to get the signal but not interfere with it on its way and then you have to get it somewhere else and not have it easily detected. This FM telephone bug is a simple start in that direction. Remember that this is just for the radio theory. This has many applications which are not illegal.

(source –

Micro Spy Listening Device

This spy circuit only contains 5 components which makes it very simple to build. For a listening device, this is very tiny but given that it is tiny, it can only transmit a limited distance.

1 – 10nF, ceramic. Preferable NPO type
1 – 20pF adjustable trimmer cap
1 – 74LS13
1 – A crystal mike
1 – Small wire for an antenna

Shoot, you are probably thinking, where do I find those parts? For the 74LS13, I would try getting it from Digi-key. Here is a link to a search I did there for it:

That is one of the possible Digi-Key part numbers. You can substitute other ones if you like. Here are the instructions on building the circuit (

FM wireless microphone circuit – FM wireless bug

Building a wearable microphone is nothing more than building a small fm transmitter circuit. This wireless FM mic is an FM transmitter and can transmit about 100 meters.

That’s not too bad of a transmission range. It is fine if you are close enough to the person wearing the microphone.  This has very few parts and can be built relatively quickly.

(source  –

FM Voice Transmitter Spy Circuit Using Band 2 VHF

VHF spy circuits or Very High Frequencies circuits can transmit for a long distance. For that reason, you should check what laws you have in your country on FM transmitters. Here is the circuit, let’s see how it is built:

There are roughly less than 20 parts for this circuit. When you are building spy circuits, why not purchase a good supply of electric microphones. I would also use a breadboard to map out some of these circuits so that you could change them around and test them. See my article on using a breadboard for more details.