
Using laser beam technology, the device, called the DNP Laser MIC allows one to pick up room audio from a distance without even entering the target room: by demodulating the transmitter IR laser beam bouncing from the target window, this equipment can receive and subsequently convert into electronic signals the slight window pane vibrations caused by acoustic waves in the room (voice speech)
Laser beam bouncing off the target window is then converted into electronic signals, then filtered, amplified and fed into a dedicated recording unit connected to its own amplifier with speaker/headphones: real-time audio monitoring and recording are possible at the very same time.
More details available at the vendor's site at http://www.eurospyshop.com/dnplongrangelasermicrophone_p_1487.html