A personal alarm
system includes a monitoring
base station and one or more
remote sensing units in two-way radio communication. An electronic
handshake between the
base station and each
remote unit is used to assure
system reliability. The remote units transmit at selectable power levels. In the absence of an emergency, a
remote unit transmits at a power-conserving low
power level. Received
field strength is measured to determine whether a
remote unit has moved beyond a predetermined distance from the
base station. If the distance is exceeded, the remote unit transmits at a
higher power level. The remote unit includes sensors for common hazards including water emersion,
smoke, excessive heat, excessive
carbon monoxide concentration, and
electrical shock. The base
station periodically polls the remote units and displays the status of the environmental sensors. The
system is useful in child monitoring, for use with invalids, and with employees involved in activities which
expose them to
environmental risk. Alternative embodiments include a
panic button on the remote unit for summoning help, and an audible
beacon on the remote unit which can be activated from the base
station and useful for locating strayed children. In another embodiment, the remote unit includes a
Global Positioning System receiver providing location information for display by the base
station.