Multi-hazard alarm system using selectable power-level transmission and localization

Abstract

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.

1 . A personal alarm system remote unit having a radio transmitter, a radio receiver, a navigational receiver, the navigational receiver providing remote unit location information, and the remote unit including a manually operated switch, wherein:
 the radio transmitter and the radio receiver comprises a cellular telephone providing a two-way communication link with a microphone and speaker connected for two-way voice communication, the navigational receiver being connected to the cellular telephone for cellular data transmission of the remote unit location information from the remote unit to a safety response center;   the cellular telephone is configured so that activation of the manually operated switch initiates a call to a predetermined telephone number of a safety response center to transmit from the remote unit to the safety response center remote unit location information provided by said navigational receiver and to open a voice channel between the remote unit and the safety response center.   
   
   
       2 . A personal alarm system remote unit as claimed in  claim 1 , wherein a plurality of manually operated switches are provided for initiating calls to predetermined telephone numbers in addition to the safety response center. 
   
   
       3 . A personal alarm system remote unit as claimed in  claim 1 , wherein the remote unit comprises timing circuits for providing time information, and a demodulator for demodulating the received navigational information, wherein operation of the switch causes transmission of the demodulated navigational information and the time information from the remote unit to the safety response center. 
   
   
       4 . A method for determining the location of a personal alarm system remote unit, the method comprising:
 providing a remote unit as claimed in  claim 1 ; and, in response to activation of said switch, initiating a call to a predetermined telephone number of a safety response center, thereby transmitting from the remote unit to the safety response center remote unit location information provided by said navigational receiver and opening a voice channel between the remote unit and the safety response center.   
   
   
       5 . A method as claimed in  claim 4 , wherein the remote unit comprises timing circuit for providing time information, and a demodulator for demodulating the received navigational information, wherein operation of the switch causes transmission of the demodulated navigational information and the time information from the remote unit to the safety response center and wherein, in response to activation of said switch, the method further comprises transmitting demodulated received navigational information and time information; and
 using computation means to combine the received demodulated navigational information and the time information to determine the location of the remote unit.   
   
   
       6 . A method as claimed in  claim 5 , wherein the computational means is provided at the safety response center and the step of determining the location of the remote unit is carried out at the safety response center.