Abstract: There is provided an alarm system for detecting and warning of the presence of alarm and trouble conditions in a plurality of zones. The system comprises a control panel having a central processing unit and a plurality of alarm devices, each having a microprocessor, that are electrically coupled to the control panel. In particular, the present invention is a two-tier monitoring system such that each alarm device monitors its zone for a shorter rolling time period and the control panel monitors the same zone of the alarm device for a longer rolling time period. An electronic circuit of the alarm device, including the microprocessor, reads and processes data received from various sensors of the alarm device. Periodically, the alarm device updates a first reference value stored in its memory based on the data received from the sensors during the shorter rolling time period.

Abstract: An alarm system in which a pair of transmission lines are disposed in a loop to define two channels of transmission from a controller to a group of interconnected detectors, the improvement comprising a spaced group of line fault isolators interleaved with respective sub-groups of detectors and connected across the lines for sensing a short circuit on the transmission lines so as to isolate the short circuit condition; the isolators including an arrangement for switching, in response to a signal transmitted from the controller, those isolators which are physically located adjacent to the short circuit without interfering with the operation of other detectors in the loop.