Wireless tether

Abstract

A wireless tether serves to warn if a tethered article moves away from the tethering location, such as a child moving away from a parent, or luggage being removed from its owner, or equipment being removed from a facility. A transmitting module on each tethered article periodically transmits a low power identification signal including a coded value. A receiving module at the tethering location receives identification signals transmitted by the transmitting module(s) and compares the coded value thereof to a stored coded value predetermined to correspond to that of the particular tethered article. If there is correspondence, the tethered article is near the tethering location. If there is not correspondence within a predetermined time interval, the tethered article has moved away and an alarm is raised. The 'length' of the tether is adjusted by adjusting the transmission range of the transmitting module to the receiving module. A number of non-correspondences may be permitted before raising the alarm so as to reduce false alarms. A receiving module can tether plural transmitting modules and may be arranged for such plural transmitter modules to have identification signal coded values that are the same, or that are partially or completely different.