The UK government has warned the Guardian newspaper that foreign agents could use laser technology to eavesdrop on them, in the wake of recent surveillance leaks. What are laser listening devices and are they effective?
When we speak, our voices produce sound waves. Sound waves travel in all directions and can hit anything in the room around you. If the sound waves hit something solid, they bounce off.
Laser listening devices are designed to pick up the vibrations produced by sound waves as they hit resonant surfaces – ones that are good for picking up vibrations – such as a window or a plastic cup.
When the laser bounces back to a receiver, the vibrations can be decoded and the conversation reconstructed.
These sophisticated pieces of equipment often look similar to cameras. A box – called a cache case, which has the technology inside – is mounted on a tripod while another box for the receiver captures the returning laser signal.
For the laser to work, there must be a direct line of sight between the operator and the target, and the laser must be within about 500m (165ft) of its target, in order to pick up the vibrations.