Silent Sentry

Abstract

NASA developed personal security system, commercialized by Sentry Products, Inc. enables resident to summon instant help in case of medical emergency or threatened violence. Its principal elements are a pen-shaped signaling device, "silent" because its ultrasonic alert signal is inaudible to the human ear, and a system of receivers interconnected with a constantly-monitored aster console. SCAN pen weighs only two ounces and is worn on necklace or attached by a clip to the user's clothing. The person in trouble simply presses a clasp, releasing a hammer inside the pen which strikes an aluminum bar. The impact causes the bar to resonate like a tuning fork and emit the ultrasonic signal, which is detected by the nearest receiver.