Patent ID: 6472986
Filing Date: 2002-10-29
Classification: G08B

Abstract:
Apparatus for raising an alarm when a separation distance between a monitored first unit and an alarm second unit exceeds a threshold, in which apparatus: the first unit includes means for wireless transmission of a signal containing identity information; the second unit includes means for receiving said signal and for causing alarm means to operate when the level of the received signal is below a predetermined threshold or when the identity information is not recognized in the received signal; and means are provided to cause the first unit and the second unit automatically to take up an inactive state and an active state respectively when they are physically connected to each other and when they are physically separate from each other, the apparatus being characterized in that:the first unit is a self-contained unit which includes encoding means for controlling the transmission of a signal in the form of periodic frames containing identity information encoded in a form that varies with each frame; and the second unit is a self-contained unit which includes decoding means suitable for recognizing the identity information in each received frame to cause the alarm means to operate over a predetermined time interval in response to failure to receive or to recognize the identity information in a frame or in a predetermined number of consecutive frames.