| 摘要 |
An intruder alarm apparatus for protecting a building or a vehicle and consuming a minimal amount of energy when in "watch" condition. An acoustic transmitter T is placed inside (or outside) a closed space S being supervised, an acoustic receiver R is placed outside (or inside) the closed space, and an amplifier A has its input connected to the receiver output and its output connected to the transmitter input. If the integrity of the closed space is broken, if for example the enclosed wall is breached at B then an acoustic feedback loop is completed by a path being thus established between transmitter and receiver, such that oscillation occurs, and only now are substantial amounts of electrical energy consumed. <IMAGE> |
