Abstract: A primary, normally open, DC monitoring circuit with a circuit continuity test device is disclosed which will also test one or more additional sensors connected to the circuit. The sensing of lack of continuity or of a fault condition detected by an additional sensor governs the status of a single indicator, generally a warning light.

Abstract: A primary, normally open, DC monitoring circuit with a circuit continuity test device is disclosed which will also test one or more additional sensors connected to the circuit. The sensing of lack of continuity or of a fault condition detected by an additional sensor governs the status of a single indicator, generally a warning light.

Abstract: A central control unit (scanner) is connected across a set of subscriber loops. At each subscriber's premises, an individual subscriber terminal unit (STU) is connected across that particular subscriber's loop. To each STU are connected the various instrumentalities which are to be monitored by the system, e.g. fire alarms, burglar alarms, etc. FSK modulated signals in the upper part of the audible range are transmitted from the scanner to the STUs at appropriate times. The STUs reply by means of similar signals to indicate the status (e.g. alarm, or non-alarm) of the instrumentalities at the respective subscriber premises. This transmission and retransmission is interrupted when the subscriber's telephone is off-hook. In addition, a signal below the audible range (low tone) is produced at the STU, and transmitted to the scanner over the telephone loop when all the instrumentalities at the particular subscriber premises are in a given state (e.g. non-alarm).

Abstract: Apparatus for indicating a break in the lines leading from a base station to a monitored instrumentality. Two pairs of wires conduct signals to each contact of a normally open switch-like element in the monitored instrumentality (the closure of which signifies an alarm condition) and return these signals to the base station. The presence or absence of the return signals at predetermined times indicates the condition of the lines and also an alarm condition, even if one of the lines leading to the instrumentality is broken.

Abstract: A central control unit (scanner) is connected across a set of subscriber loops. At each subscriber's premises, an individual subscriber terminal unit (STU) is connected across that particular subscriber's loop. To each STU are connected the various instrumentalities which are to be monitored by the system, e.g. fire alarms, burglar alarms, etc. FSK modulated signals in the upper part of the audible range are transmitted from the scanner to the STUs at appropriate times. The STUs reply by means of similar signals to indicate the status (e.g. alarm, or non-alarm) of the instrumentalities at the respective subscriber premises. This transmission and retransmission is interrupted when the subscriber's telephone is off-hook. In addition, a signal below the audible range (low tone) is produced at the STU, and transmitted to the scanner over the telephone loop if, but only if, all the instrumentalities at the particular subscriber premises are in a given state (e.g. non-alarm). If not, low tone is stopped.

Abstract: A central control unit (scanner) is connected across a set of subscriber loops. At each subscriber's premises, an individual subscriber terminal unit (STU) is connected across that particular subscriber's loop. To each STU are connected the various instrumentalities which are to be monitored by the system, e.g. fire alarms, burglar alarms, etc. FSK modulated signals in the upper part of the audible range are transmitted from the scanner to the STUs at appropriate times. The STUs reply by means of similar signals to indicate the status (e.g. alarm, or non-alarm) of the instrumentalities at the respective subscriber premises. This transmission and retransmission is interrupted when the subscriber's telephone is off-hook. In addition, a signal below the audible range (low tone) is produced at the STU, and transmitted to the scanner over the telephone loop if, but only if, all the instrumentalities at the particular subscriber premises are in a given state (e.g. non-alarm). If not, low tone is stopped.