I bring to your attention a spy radio microphone with extremely low power consumption. This is perhaps the longest lasting bug I have ever collected.
Of course, you have to pay for the low power consumption with a short range, but for many purposes this is quite enough.
The radio microphone confidently penetrates two reinforced concrete walls, and in open space the range will be from 50 to 200 m (depending on the steepness of your receiver).
The bug's circuit is incredibly simple and contains only 6 radio components, not counting the battery:
Coil L1 - 4 turns with 0.5 mm wire on a Ø2mm mandrel. Choke - 100 nH for surface mounting. Transistor BFR93A (the main thing is not to confuse it with the pnp transistor BFR93).
and etched in ferric chloride: 
All this took about 20 minutes. Then I tinned the finished board and cut off the excess: 
The most difficult thing is to connect the battery. I had at my disposal an old (!!!) CR2032 lithium battery (which is usually found in motherboards to power the BIOS chip).
To avoid unnecessary wires, I simply glued a strip of tin from a tin can to the back of the board (this will be the negative contact): 
The remaining piece of tin was useful as a positive terminal: 
The battery must be tightly inserted into the resulting slot, like this: 
All that remains is to solder all the parts onto the board according to the diagram: 
I'm sure it can be made even smaller. Replace the microphone, place the parts closer together, take small watch batteries and you're done. It will be possible to stuff the entire circuit, for example, into the body of a marker.
I used a 6 cm long wire as an antenna. The choke was made by winding a thin enameled wire on a piece of toothpick (80 turns). 
The microphone, of course, is too big for such a circuit, but I didn’t have anything else. In general, any electret with a diameter of 3-10 mm will do. Usually they are taken out of any telephone or intercom handsets.
By the way, the circuit does not work without a microphone - power goes through it. It also acts as a current stabilizer.
It is important not to confuse the polarity of the microphone: the negative terminal should ring into the body (that is why I put it in heat shrink, so that God forbid, nothing short-circuits). 
The frequency is adjusted by compressing/stretching the coil turns. In my case, the bug was caught at a frequency of 424.175 MHz. The signal level at such a distance, naturally, goes off scale: .jpg)
If you wind 11 turns on a 2 mm mandrel, the frequency will be approximately 150 MHz. In general, this bug works up to 1 GHz. I didn’t try further, because... nothing to catch.
To test the range, I went outside and walked around the house. Amazingly, in the room where the bug remains, every rustle is clearly audible.
P.S. This tiny bug worked on a half-dead battery for almost 2 weeks! It’s scary to imagine how long it would last on a new one, because the current consumption is only 300 µA. 
It's not good to eavesdrop. But there are situations when you need to know what is happening in a small child’s room or in class at school. This requires homemade wiretapping, using the most current method of transmitting information - ordinary radio waves.
The necessary device can be purchased in a store or ordered online. But a high-quality device will be expensive, and a cheap Chinese product will quickly fail. Therefore, it is more practical and cheaper to make a wiretapping bug yourself.
This is quite achievable. You will need a little ingenuity and skill, as well as inexpensive components and a circuit diagram for a simple wiretapping bug. It is not necessary to buy suitable parts in a store; old ones soldered from electronic equipment are quite suitable.
A very interesting miniature device for passing exams. Even a beginner can assemble it. It consists of an earphone and a transmitter.
Below is a working diagram of a DIY bug for listening:
1. Transmitter
2. Micro earphone.
Schematic diagram of a basic bug for listening
The advantage of this device is its miniature size. The earphone inserted into the ear is completely invisible from the outside. The range of the device is at least 100 meters
Here is a more complex radio bug circuit for wiretapping using a 1.5 V battery and a transmission range of at least 100 meters.
Diagram of a radio bug with a range of up to 400 meters
You need to pay attention to one distinctive feature of the plan - the impulse to the antenna is supplied from the electrode of the bipolar transistor, which allows you to stabilize the operating frequency of the device.
Collecting a radio bookmark
The result is a small and easy-to-make homemade wiretap that can be easily hidden in an inconspicuous place. However, this model has a small drawback - the antenna is 50 cm long. This is not entirely convenient if you want to hide the device as much as possible.
Connecting components according to a given diagram
How to make a radio bug for listening:
- Let's cut a rectangle measuring 53 mm by 75 mm from thin plywood or textolite. Homemade wiretapping will be based on it;
- we will make coil L1 from copper wire with a cross-section of 0.3–0.5 mm, winding eight turns onto a knitting needle with a diameter of 30 mm and leaving the ends 1.0 cm;
- From the same wire we will weave two two-terminal networks C2 and C3. Each is 1.8–2 cm in size. We straighten the upper ends in different directions and tin the lower ends;
- for the choke, take a copper wire with a cross-section of 0.05–0.1 mm and wind it tightly onto a match. The height of the wrap is approximately 6–7 mm. We cut the match to a length of 1.0 cm, make slits at the top and bottom in which we secure the ends of the wire;
- The antenna is made from a cable 50 cm long in plastic insulation, wound in a spiral.
You can buy a microphone at a radio store or take it from an unwanted cell phone. To correctly position the parts on the base, you will need a wiretapping bug diagram. Let's transfer it to plywood. According to the drawing, we will make holes for the parts and insert them. On the opposite side we solder all the parts strictly according to the diagram.
Terms of use
Let's look at how to use a wiretapping bug. Since the device transmits on standard broadcast frequencies, it can be heard by any transistor or cell phone.
Having assembled the device, turn on the FM radio and look for the bug signal. It is not difficult to distinguish it from other FM sounds. When you rotate the receiver knobs, clicks should be heard. The loudest sound will be the signal of the radio bug. Then we set the device to the selected range.
Well, in the end, we need to remind you that a homemade wiretap can only be used as a home toy for hidden radio surveillance of an apartment, or as a baby monitor for a child. You should not break the law.
On the Internet you can find a huge number of radio bug circuits. Some circuits are too complex and require configuration, others include scarce radio components, and still others don’t work at all!
I bring to your attention a diagram of a bug that can be assembled by both an experienced radio amateur and a beginner in this matter.
Let's look at this diagram:
Ignore the dotted line for now.
To make a bug we will need the following parts:
- VT1 - kt315 with any letter index (if you want to increase the range of the bug, it is better to use a microwave transistor, for example kt325 or kt368, the imported transistor s9018 is perfect);
- C1, C4 – 47...68nf;
- C2, C3 – 10pf;
- R1 – 33 kOhm;
- R2 – 100 Ohm;
- Oscillatory circuit L1 - 8 turns of copper wire with a diameter of 0.3...0.5 mm on a rod from a helium pen, wind carefully, turn to turn (I unsoldered the finished coil from a broken radio).
- M1 – electret or condenser microphone.
To save space, I used the right microphone (I found it in an old cell phone). Despite its size, it turned out to be very sensitive.
All parts except the L2 choke and microphone are shown in the following picture:
To make L2 we need a match and very thin wire:
We measure one and a half centimeters of matches, bite them off - this piece will serve as the core of the choke. Next, take the wire and wind one hundred turns. We fix the terminals of the resulting coil, clean it of varnish, and tin it. That's it, throttle L2 is ready!
When all the parts are assembled, you can start making the printed circuit board.
To do this, we need a 35x15mm piece of PCB and the solution itself in which we will etch the board (I used hydrogen peroxide + citric acid). Making a drawing of the printed circuit board (I drew it for the s9018 transistor)
and transfer it to the textolite.
Place the board in the solution and wait until the excess copper disappears.
After the board is etched, we take it out, rinse it with running water, remove the varnish and tin it:
Next, solder the parts in accordance with the diagram. Attention, when installing parts on the board, do not overheat them, otherwise they will fail! Be especially careful when installing VT1.
I would like to say a few words about connecting the antenna; the signal is supplied to it from the emitter of the transistor, which makes the operating frequency of the bug more stable.
Assembled diagram:
The bug can be powered in the range from 1.5 to 9 volts.
Any of these batteries will be suitable to power the circuit. I used a AAA AA battery to make the bug more compact. You can also use a 3-volt “pill”.
If you will power the circuit from the crown (9 volts), then you should include a 100 Ohm resistor R3 in the circuit.
Carefully solder the battery to the bug. An insulated wire 30 cm long can be used as an antenna, but practice has shown that its absence will not greatly affect the reception range of the circuit. That's it, the bug is ready!
Now turn on the radio and look for the frequency of our bug. The signal from it can be caught at a frequency in the range of 88-108 MHz. For me this frequency was 92.2 MHz. If the bug “does not communicate,” then try moving apart the turns of coil L1 - this should help solve the problem.
With a supply voltage of 1.5 volts, the reception range is 30 meters; if you increase the voltage to 3 volts, the reception range will increase to 100 meters.
This circuit also has another application - an audio transmitter. Let's say you need to output sound from your phone to a tape recorder, but the latter does not have an audio input function. No problem! In this situation, this scheme is very useful. Almost all tape recorders have a radio reception function (FM radio), which is what we will use. Remember the dotted line on the bug diagram? We exclude microphone M1 from the circuit, connect capacitor C5 to a capacity of 10 μF, connect a 3.5mm mini-jack plug to the minus of the capacitor and the minus of the power supply (minus of the jack to the common one, left/right to the minus of the capacitor) and transmit sound from the phone to any radio receiver located within the range of the transmitter! If the parts are installed correctly, the circuit begins to work immediately.
These products can be used for a variety of purposes: from indoor listening to wireless sound transmission.
And this is where my article comes to an end, good luck to everyone in repeating!
Although making listening devices, so-called “bugs,” is illegal and faces criminal liability, for the inquisitive mind of a radio amateur, this is not an obstacle for self-education and interest; in addition, such a device can simply serve as a radio microphone for a karaoke system. This simple bug, which is assembled on just one transistor, operates in the VHF range from 80 to 108 MHz, and is received on a regular FM radio.
Its sensitivity is quite good and depends on the electret microphone used, since there are both good electret microphones and not so good ones, for this you will have to choose a similar one with better sensitivity, and the sound will be clear and not distorted. The bug's range is up to 50 meters, depending on the length of the antenna and the transistor used. The only obvious drawback of such a circuit is that it unstablely maintains the frequency as the battery discharges, because this is the simplest radio microphone circuit, without quartz frequency stabilization, so it is better to choose a power source with good capacity.
Parts you will need to make an FM bug:
- A small piece of foil fiberglass or breadboard;
- Transistor KT368 or BC547, KT3102, S9018, with the last transistor the power and range of the radio microphone will increase;
- Microphone (suitable for any Chinese tape recorder);
- Resistor R1 – 4.7 kOhm;
- Resistor R2 – 270 Ohm;
- Capacitor C1 – 1nF;
- Capacitor C2 – selected depending on the frequency;
- Capacitor C3 – 4.7pF;
- Capacitor C4 – 100nF;
- A piece of wire 20–40 cm long as an antenna;
- Power source: 3V battery - CR2032 lithium tablet or 3.7V battery.
How to make a simple FM bug, step by step instructions:
We take a piece of the board and use a sharp knife to cut out the tracks, you can also etch them out, but since this is a simple bug circuit and the board turns out to be tiny, I decided to cut out the tracks with a scalpel. You can also solder everything on a small piece of breadboard.
We wind the coil L1, for this we need a wire in varnish insulation with a diameter of 0.4 to 0.6 mm, we wind it on a mandrel with a diameter of 4 mm, for which a rod from a helium pen is a good choice, we make 12 turns around the mandrel.
We solder all the parts onto the printed circuit board, when soldering the microphone, pay attention that it has a connection polarity and you must not confuse them, in order to understand which pin needs to be soldered to the minus, and which to the input of the transistor you need to look at it from the terminals side, where The output has tracks leading to the aluminum case, this is a minus, the opposite one, which does not touch the case, is a plus and must be connected to the base of the transistor.
A flexible piece of wire from 20 to 40 cm long serves as an antenna. The longer it is, the greater the distance the bug will be able to transmit sound.
Setting up a radio microphone is very simple; to select the transmission frequency, you need to select the capacitance of capacitor C2; here are approximate correspondences of its capacitance to the frequency in FM:
- 10p – 88 MHz;
- 8.2p – 95 MHz;
- 6.8p – 104 MHz.
Also, the frequency is adjusted by stretching the turns of coil L1.
The consumption of the entire circuit is not large, about 5-7 mA, and therefore a flat lithium battery is suitable as power supply - a CR2032 3 volt battery or, even better, a 3.7 volt battery, for example from a cheap Chinese mp3 player, it is small and has enough capacity. You can also choose a suitable case for it, small and convenient.
That's it, our simplest DIY FM bug on one transistor is ready, all that remains is to connect the power, set the radio microphone frequency on the receiver and enjoy the result.
A wiretapping bug is a simple radio transmitter with a microphone that picks up the slightest sounds around it and transmits them through a radio wave. Thus, by leaving such a device in a suitable place, you can listen to everything that is happening around it.
You can find many uses for a wiretapping bug - for example, using it as a baby monitor, wireless headphones, or simply to eavesdrop on someone's conversations (it is worth considering that such use is illegal). If you assemble two radio transmitters, you can organize wireless communication, for example, between neighboring houses.
There are a large number of bug circuits for listening on the Internet - from the simplest to the most expensive and complex, built on microcircuits. The diagram below is one of the most optimal: it does not require rare or expensive parts to install the device, but the bug itself will have a good signal transmission range (up to 500 m) and high stability.
Wiretap bug - diagram and necessary radio elements
The circuit includes three cascades:
- The microphone audio signal amplifier is built on transistor VT1.
- The carrier signal generator is made on transistor VT2.
- Transistor VT3 is a high-frequency amplifier; it is responsible for good transmission range.
- VT1 - KT3130B;
- VT2 - KT368A;
- VT3 - KT3126B.
Coil L1 is wound with copper wire on a mandrel with a diameter of 3 mm, 6 turns. The wire can be taken with a cross-section of 0.3–0.4 mm. You can use a regular drill as a mandrel.
L2 - choke, inductance 100 μH. It is best to use it ready-made. An ordinary piece of wire will do as an antenna, but if there is a need to achieve maximum transmission range, it is advisable to use a wire one-quarter the length of the wavelength at which the transmitter operates.
- You might also be interested in how to do
Files for download:
Assembling a bug for wiretapping with your own hands - instructions and photos
The circuit is assembled on a printed circuit board measuring 70x30 mm; the LUT method is used for its manufacture. There is no need to mirror the board before printing. Below are some photos of the process.
After the copper is etched, the holes are drilled, the tracks are tinned, the parts can be soldered. Particular attention should be paid to the microphone, or more precisely, its polarity. One of its contacts is short-circuited to its body - this particular contact is negative, it is soldered to the negative of the circuit.
- See also the diagram of professional
Tips for setting up and trial run of a bug for wiretapping
For the first start you will need a milliammeter. To control the current consumption, it is connected to the break of one of the supply wires. We connect the crown and watch the readings of the device - the current should be in the range of 10–30 mA. If it is normal, you can turn on the radio and try to find the signal of the transmitter being tested.
Most often, the signal is already in the range of 80–110 MHz. If it “creeps” beyond this range and the receiver cannot catch it, you should adjust the L1 coil by squeezing and unclenching its turns. The transmission frequency depends on the inductance of this coil. When the signal is found, the coil can be filled with dielectric varnish or epoxy resin so that the tuning is not lost.
It is very important to ensure that the broadcast frequency of the assembled transmitter does not overlap with the frequency of any radio station. If they intersect, then you need to change the frequency by adjusting the L1 coil. The bug does not require any further configuration; you just need to adjust the broadcast frequency. Now you can test it for signal transmission range, moving with the pocket receiver further and further from the transmitter itself. A properly assembled and configured transmitter can provide a transmission range of up to 500 m in open areas. It should be taken into account that the reception range also depends on the sensitivity of the receiver. Happy building!
A simple bug for wiretapping at a distance of 100 meters with your own hands
Below is the design of a radio transmitting device with a range of up to 100 meters. Such a bug is built according to a three-point capacitive circuit (like all other known circuits). The frequency does not float, as happens in many wiretapping bug schemes. If you stand with the receiver at a distance of 1, 10 and 50 meters from the beetle, then the frequency shift will be only 100–120 kHz - which, you see, is very small and cannot affect the quality of listening.
Below is a diagram of a bug for wiretapping:
This bug can be used for targeted wiretapping of rooms and even moving objects! This became possible thanks to the selection of transmitter components, which makes the modulated signal quite stable, and the circuit at the same time remains simple and accessible even for a novice radio amateur.
The transmitter can use low-power RF and microwave transistors. It is advisable to use transistors with a cutoff frequency of 700–1000 MHz. The domestic KT368 (which is a complete analogue of the transistor indicated in the circuit) is perfect.
To increase the sensitivity of the radio microphone, an additional microphone amplifier was used, the circuit of which was built on just one transistor.
Literally any low-power transistor - KT3102, KT315, KT368, S9014, S9018 and others similar. Such an amplifier makes it possible to pick up even a quiet whisper in a room of 16 square meters. m. The sensitivity of the bug is about 5 meters.
The antenna is a multi-core wire 10–25 cm long in rubber insulation.
The coil consists of 5 turns, wound on a frame with a diameter of 3-4 mm. You can use the paste from a gel pen as a frame. A wire with a diameter of 0.5–1.2 mm (in our case 0.8 mm) is suitable for the circuit.
You can use almost any electret microphone; sensitivity is not very important, since the bug has an additional microphone amplifier.
- Find out also how to make an electret microphone on a chip
To tune to the desired frequency, a variable capacitor was used, which, after full tuning, was replaced with a constant one (capacity 18 picofarads). By rotating this capacitor you can tune the bug to the frequency you need.
The beetle operates at frequencies of 96–99 MHz and is caught on a regular FM receiver. With a high-quality receiver, you can catch bugs at a distance of up to 150 meters.
This is what a wiretapping bug looks like:
Video on how to make a simple bug with your own hands: