The main type of laser microphone is a surveillance

Surveillance

Surveillance is the monitoring of the behavior, activities, or other changing information, usually of people. It is sometimes done in a surreptitious manner...

 device that uses a laser

Laser

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

 beam to detect sound

Sound

Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...

 vibration

Vibration

Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...

s in a distant object. The object is typically inside a room where a conversation is taking place, and can be anything that can vibrate

Vibrate

Vibrate may refer to:*Vibration*"Vibrate," a song by Outkast from their 2003 album Speakerboxxx/The Love Below*Vibrate, a song by Rufus Wainwright from his album Want One*Vibrate , the 2004 album by The Manhattan Transfer...

 (for example, a picture on a wall) in response to the pressure waves created by noises present in the room. The object preferably has a smooth surface. The laser beam is directed into the room through a window, reflects off the object and returns to a receiver that converts the beam to an audio signal.