Abstract: An alarm signalling method and system utilizing cross cueing between radio, audio and visible alarm signals which are emitted by an alarm signalling unit. A method and system for measuring the range between the alarm signalling unit and a receiver carried by a rescuer wherein the differences in the time of receipt at the receiver of simultaneously emitted radio and audio signals is used as a measure of range.

Abstract: An emergency signalling unit which is designed to be carried on the person of a fireman or other worker to alert control personnel should the worker become endangered, and an alarm system which incorporates a plurality of such signalling units, each one worn by a different fireman, for providing an alarm at a central station and an indication of which fireman is in trouble, as well as a means of locating him. The emergency signalling unit includes a radio transmitter, a high intensity strobe lamp, and an audio frequency generator. The alarm system includes a plurality of the above-mentioned radio transmitters, each transmitting on a different carrier frequency, and a receiver at a central control station exterior to the burning building, which is equipped to identify the respective carrier signals and to provide a visual indication of which fireman is in trouble as well as an audible signal to alert control personnel to the existence of an alarm condition.

Abstract: A device for installation to a telephone which prevents the telephone from ringing except for incoming calls from selected individuals who have been furnished a key device. The key device emits an audible tone into the mouthpiece of the calling telephone which signals the installed device at the called telephone location to accept the call and actuate the called telephone bell or signal. The installed device is connected to the telephone wire of the installed telephone with electronic circuitry that disconnects the ringing current circuit to the installed phone immediately upon the appearance of the ringing current on the phone line, thus preventing ringing of the called telephone bell. The device then sends an electrical signal, which is recognizable as an audible tone, in the receiver of the calling telephone.

Abstract: A housing is supported in front of a conventional female wall socket by a conventional two-prong male plug that extends out the rear of the housing and engages the socket. A flag is pivotally secured to the housing and can be pivoted into or out of it in a vertical plane parallel to the wall socket. Normally the flag is retained in the housing. When there is an interruption in the supply of electric power to the socket, the flag will pivot out of the housing automatically.