Spy devices for contact and contactless information acquisition

We make a spy device with our own hands from available tools

There are many different ways of spying. Surely each of you has heard about listening with a laser, either through radiators, or using microphones mounted in the walls of a building. And all this is shrouded in some mystical meaning, although in fact it is simple and accessible for everyone to understand and repeat. And most importantly, everything is assembled from improvised means.

Once in the shaggy years, in one popular IT-publication I wrote a similar article, but probably did not really reveal the essence of exactly how it works and how to use such devices. And let's be honest, the version that I gave in the article looked cool, but was not very workable.

The "spy" device of that time

As a result, I decided to make it myself and demonstrate how it works.


Before we go any further, we must understand that the manufacture and use of spy devices falls under the articles:


  • RF Criminal Code Article 138.1. Illegal circulation of special technical means designed to secretly obtain information.
  • Criminal Code of the Russian Federation Article 137. Violation of the inviolability of private life.
  • RF Criminal Code Article 183. Illegal receipt and disclosure of information constituting commercial, tax or banking secrets.

Thus, everything that is presented in the article is only a demonstration of the possibilities, serves solely for information! It should be well understood that the repetition and use of the methods described in this article can lead to very real terms of imprisonment.

I will say for myself that I did not try to spy on anyone in any way, as I consider it at least unethical. I just played in the room and in the kitchen, recording myself. Don't be naughty, I warned you!

Cooking iron

The device we are going to make is called a banally contact microphone. It is not prohibited in any way, there are a lot of instructions for its manufacture on the Internet, but few people know that it can be used to secretly obtain information. To make it, we need: a piezo speaker for voice frequencies (anyone operating in the range between 300 and 3400 Hz), a matching resistor, some wires and maybe even a soldering iron, but at first I did even without it. Everything was purchased from a renowned amateur radio boutique.


I wanted to use a mobile phone as a recording device. But, as it turned out, he determines the headset by resistance. I didn't have these resistors, and the second time I went to a fashion boutique was too lazy. However, I will tell you how to do this, you never know who wants to record mystical sounds - this is quite legal. It is necessary to assemble the equivalent circuit of the headset.

Electrical circuit of the telephone headset

So that the phone detects our contact microphone, it is necessary to solder 30 Ohm resistors in place of the speakers, and a 1.5 kOhm resistor in place of the microphone in parallel to the piezodynamic device. Why so, I'll tell you a little later.

For my experiments, I chose an old cassette recorder, which I dug up on the mezzanine by chance. We will connect our contact microphone instead of the audio head of one of the cassettes. For all the absurdity of this solution, it has one huge plus: very high sensitivity, because the head must register barely noticeable magnetic pulsations of the audio cassette. And we get a finished amplifier.


It was with great difficulty that an audio cassette was purchased in the center of Moscow to record audio. Blank cassettes are like a cast-iron bridge, I had to buy with a recording.

Honestly listened to both sides of this cassette, wiping nostalgic tears from my face and blood from my ears. As a result, I concluded that the future generation will not lose anything if I erase it.

I disassemble the tape recorder and inside I see how three heads (one for recording) come to the motherboard of the tape recorder. The playback heads have three pins: left, right, and ground (usually braid). I unite the left and right channels, and throw the earth onto the braid in the same way. Shielded wires must be used, otherwise there will be a very strong hum of interference (we have a highly sensitive amplifier).

Dissecting the subject

Head connector

From scrap materials I make a connector instead of the standard head of the right cassette player, install it in place.

Ready connector

Now let's talk about the sensor. A bit of theory at the level of school physics. The magnetic head, as you might guess from its name, is a very low resistance inductor . When the tape is being pulled, a very small EMF is induced in it and gets to the amplifier. In fact, the magnetic head can be thought of as a voltage source in series with a resistance. A piezo speaker is, in fact, a capacitor with a very high ohmic resistance (can be considered equal to infinity), which is a current source and gives current regardless of resistance. By the way, therefore, piezoelectric elements have found application in lighters: they will give strictly small current, regardless of air resistance, while the voltage can grow to enormous sizes.

I got distracted. My task was to make an equivalent circuit of a magnetic head (read EMF + resistance) from a current source. Those who know the Theoretical Foundations of Electrical Engineering well understand what I mean. And for those who did not understand, see the diagram below.

Equivalent circuit

Thus, it is enough to solder the equivalent resistance in parallel with the piezoelectric sensor and the trick is done. In my case, it was about 50 ohms. But I'll be honest, I soldered the first resistor I came across in the house, but it worked.

Our ready-made contact microphone

Everything is ready for evil experiments!

Demonstration of work

It is better to see and hear how it works once than to read it a thousand times. Therefore, here is a video, and then we will analyze how it all works.

In this video, I've covered the basic principles of espionage. All of them are based on the fact that bodies vibrate due to sound vibrations. Of course, vibration occurs at the natural frequency, but if you remove it with a mathematical filter or an analog filter and normalize the signal, you can get the original voice signal. This is the principle behind espionage using communications or microphones embedded in walls, espionage by laser picking up the vibrations of glass, picking up the vibrations of lighting lamps, and even the famous spy device at the US Embassy. Let's take a closer look at all these methods.

Listening by intercepting the oscillations of the lamp light

There is an excellent article (English) that describes how it works and shows a video of such espionage.

Screenshot from the video demo

In my video I have already described the principle of operation. You can use the same microphone, just replace the piezoelectric sensor with a resistor with a phototransistor or photoresistor (additional power may be needed), or just a solar battery. Perhaps I would repeat this experiment, but the optics are missing. Therefore, I will tell you purely theoretically.

The plafond of any lamp has a natural frequency. When we speak next to him, we stir up his vibrations. Visually, we cannot see them, but from the street it is quite possible to record these oscillations using a telescope, illuminate any optical sensor with it and digitize. The camera could have been fitted, but it must shoot at least 22,000 frames per second. Therefore, we just take any photocell. Then we digitize this data. filter, normalize, remove noise and get the original. The filtering method is suitable for all other secret information retrieval methods. In any case, I recommend everyone to read the article in more detail.

Spying with laser and window

The method is legendary and old. But it is very simple and accessible to any student. We take the same device as in the previous chapter. But instead of a telescope, we have a laser.

A person is in the room, talking, and the glass in the window echoes his speech at the natural frequency. We irradiate the glass with a laser beam and take it back. Then you know the algorithm. The problem with this method is obvious: there is not always room for the correct placement of the laser source and receiver. Therefore, it is not very actively used and is used only where the terrain allows.

Eavesdropping method through communication

In general, without any technical means, put your ear to your battery on a weekday when children from neighbors are yelling, dogs are barking, etc. And it turns out that the pipes, even when embedded in the wall, perfectly transmit sound.

The battery begins to resonate at its natural frequency, and the metal perfectly transmits sound waves over very long distances. Next, you need to fix the sensor well. By the way, my magnet mounting method is not the best. It is necessary that the piezoelectric sensor has a mass clamp so that it is well deformed from vibrations; and in such a way that the area of ​​its contact is maximal. In my case, he contacted a small area with both the lamp and the battery. I think that's why the sound was not very good.

Removal of vibrations of objects using radio waves

It may seem that this is something from the category of fantasy. But nevertheless, in this way, the famous espionage for the US Embassy was carried out, when the pioneers presented the ambassador with a coat of arms and he hung it in his office. And in this coat of arms there was a bug that did not have any electronic devices.

The famous spy coat of arms

On Habré there was already an article about this bug, but there it is very scanty about the principles of its action. It is arranged very simply.

In fact, the membrane picks up sound vibrations and changes the geometry of the antenna! In the house opposite, there is a transmitting device that broadcasts at 330 MHz. It just generates a pure sine. The receiving antenna is irradiated by this field, changes its geometric dimensions and re-radiates a modulated echo. Everything, it remains only to accept it. This principle is called “high frequency imposition”. The best way to see how this spy device works can be seen in the video below.

Thus, even a knitting needle, if properly secured and of a certain length, can be a spy device. And this is not irony or an attempt to intimidate, but a harsh reality.


Want to feel like a real spy from the comfort of your couch? I have a game for you. Specially for you I recorded a speech performance, with a fixed contact sensor on the lamp.

Sound file and program for experiments

The task is to figure out what I'm saying there. You do not need to send a transcript, you can simply name the work that I am reading in the comments. The file itself is here .

I think any sound engineer can do this easily. At the very beginning, I specifically click on the lamp (on the overload screen at the beginning) so that you can determine the frequencies of the lamp's natural oscillations, and then select my voice. Good luck!

How to live on?

If you are not paranoid, this does not mean that you are not being followed!

"Motherland hears" thin. Vasya Lozhkin

What to do to not be followed? In serious organizations, meeting rooms for particularly important meetings are magnetically protected, and they are also lined with sound-absorbing materials and do not have windows. However, about you and me, you can say in words from an anecdote about the elusive Joe: no one really needs him. I don't think we should think that we are all being watched. And if they do, that is, there are simpler ways of spying, you, everyone has such a wonderful bug in your pocket and everyone who needs to know everything about you. Don't worry and sleep well.

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