Photosensitive alarm systems

US4242670A · kind A · utility

Inventor

• William V. Smith · Memphis, US

Key dates

• Filing date: Mar 2, 1979
• Grant date: Dec 30, 1980
• Expiry date: Mar 2, 1999

Classification

• Technology area (CPC G): Physics
• CPC primary: G08B25/10
• WIPO field: Control
• WIPO sector: Instruments

Abstract

A photosensitive alarm system is provided which produces an alarm signal upon exposure to ambient light for protection of cash drawers, file cabinets, and shipping or storage containers from unauthorized intrusion. The alarm system includes photosensitive arming and trigger circuits which allow the system to become armed when placed in darkness and to be subsequently triggered when exposed to the ambient light. The arming and trigger circuits include separate photocells which are arranged to draw a minimal current to allow a DC battery to be used as a power source for an extended period of time without need for recharging or replacement. Preferably, the alarm system includes a warning circuit capable of producing different output signals in response to multiple exposures of the trigger circuit to the ambient light to indicate the number of intrusions and a clock circuit for indicating the time and date of the initial intrusion into the protected area. Alternatively, the system includes a plurality of intrusion detectors each having a warning circuit which generates unique identification signals to specify the location where the intrusion occurred.