The Science Museum in London has a receiver unit on display.
The beam reflected off the pane and bounced back to a receiver unit.
While she was speaking, her fingers adjusted the receiver unit in her ear.
Usually, there are separate transmitter and receiver units at either end of a straight beam path.
The receiver unit can be programmed to emit a warning beep at a certain pressure level.
Such systems cost about $200 to $400, plus installation of the sensors and receiver unit.
The least expensive systems usually have a passive subwoofer, which is amplified by the receiver unit.
He'd spotted two of the receiver units about three hundred yards apart.
The other audio equipment is connected to the receiver unit by cable.
