Installation for transmitting alarm signals

US4347501A · kind A · utility

Assignee

• Telefonaktiebolaget LM Ericsson (Publ) · SE

Inventor

• Dag E. Akerberg · Hagfors, SE

Key dates

• Filing date: May 15, 1980
• Grant date: Aug 31, 1982
• Expiry date: May 15, 2000

Classification

• Technology area (CPC G): Physics
• CPC primary: G08B25/016
• WIPO field: Control
• WIPO sector: Instruments

Abstract

In an installation for transmitting alarms, preferably in connection with attacks on persons, and for locating the alarm sender, there is at least one portable alarm sender 2 sending an alarm to a central alarm receiver (3) by radio. The senders each contain a memory (24) for a code unique to their position in the installation. The code is automatically set by fixed transmitters (1) having a small range, which transmit it electromagnetically, especially inductively, to the sender (2), the code being unique to the location of a transmitter and stored in the sender memory. When fixed transmitters (1) are arranged so close together that their unique codes are difficult to separate in the sender (2), a dummy transmitter (56) is arranged to prevent alteration of a code already stored in the memory (24) of the alarm sender, as long as the sender (2) is close to the dummy transmitter (56). The sender (2) also transmit a second code stored in a second memory, unique to the individual alarm sender and thereby to the carrier of the alarm sender.