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Can we listen with a laser?

When listening devices have been created? . Most likely, when people realized that it is cheaper to invent a technical gizmo, you can use your own ears.
Currently, there are many ways to listen to and removal of acoustic information from the objects of interest. Special vehicles for covert listening devices record and receive voice data to date is presented in abundance - recorders, embedded devices, directional microphones, and even lasers! . In this case, use the special facilities - laser systems acoustic intelligence ( LSAR ).
The laser system consists of an acoustic investigation of the laser transmitter in the infrared and optical receiver. The laser beam through the optical sight is directed to a window area in which the attacker being interested in talking. When the laser beam reflected from the vibrating surface is modulated acoustic signal of the angle of the reflected laser beam and its phase.
Laser systems of acoustic intelligence can be built on two standard schemes, ...
In the ... On the border of the glass -air environments beam is modulated by sound vibrations. Further, the reflected beam falls on the photodetector, which is located so that the angle of the reflected beam was equal to the normal average angle of the incident laser beam. At the photodetector, is the amplitude demodulation of the reflected beam. The system is complex because it requires alignment. Therefore, rarely used.
In the ... The principle of operation of LSAR is based on the differential method of measuring acoustic vibration. Such systems do not require adjustment.
The theoretical possibility of LSAR range from hundreds of meters to 1 km. In practice - it all depends on the specific conditions of the equipment space. For example, the level of the external acoustic noise can be quite high, in connection with the fluctuations of the external glass double glazed windows under the influence of street noise will exceed the amplitude of oscillation of acoustic speech signal. Location LSAR with respect to the sensed object plays an important role in the success of listening. LSAR achieved better performance while providing a laser beam perpendicular to the surface of the irradiated glass. It is not always possible to create an environment of information retrieval. It should be noted the difficulty of obtaining information using LSAR information, if the window will be opened periodically.
Considering the mass of LSAR (3-10 kg without batteries and tripods ), this creates additional disadvantages in their application.
Now LSAR produced mainly by foreign productions. And the cost of such systems from $ 10,000 to $ 130,000. It should be noted that the effectiveness of such a system increases as the light of operational space.
The use of complex LSAR requires high professionalism. It is known that the LSAR used against the Soviet embassy staff and consulates in the U.S.. Overheard conversations in families of their employees by place of residence. It can be assumed that Western intelligence agencies are able to covertly use such devices, and in Russia in the framework of competition.

Protection against laser microphone with his hands.

Places your office can listen in many ways, one of which is the resonance window panes. But even the laser detector can put an obstacle.
Figure 1 shows a circuit modulating the glass. Resonating element is a piezoelectric element which is rigidly mounted in the center of the glass to ensure maximum amplitude. The scheme collected on TTL chips that consume a lot of current, and therefore must be used to power the power supply unit. Piezoelectric sensor modulates the glass so that the amplitude modulation of the glass is higher than the modulation of the voice, with an average volume of pronunciation. In addition, the piezoelectric element modulates the glass at different frequencies, which further complicates the removal of information through the glass.
Proposed and a simple circuit disruption listening ( Figure. 2 ).
As a modulator of c 50 Hz using conventional small-sized DC relay REF 22, REF 9. The winding connected to the AC voltage just below threshold. The relay is secured to the glass adhesive EPD.

You can also try very rudimentary scheme for the protection of the LSAR.

We all know the law of physics - ' angle of incidence equals angle of reflection '.
This means that we should be exactly perpendicular to the window listening room. From the front of the apartment you are unlikely to catch the reflected beam, as the walls of the building normally, I 'm not talking about a window, a little crooked, and the reflected beam will pass you with a tolerance of 1 to. meters.
Before an important meeting of the slightly open window, and while spies running around the neighboring buildings and the reflected beam are looking for, you probably have time to discuss all the important moments, and if you change the position of the window every 5-10 minutes ( slightly open, close), then all of a desire to listen to you after a marathon .
The problem of anti- readout using laser radiation is very relevant and at the same time, one of the least studied in comparison with other, less ... The special attraction of such systems due to the fact that they allow to solve problems of removal of the speech information as safe a distance, indirectly, avoiding the need to call in the room of interest to the deployment of a listening device that is always associated with risk. In addition, and identification of operating a laser microphone is very difficult, and in some cases technically feasible.