The line isolator is a bidirectional non-addressable loop monitoring device for addressable fire detection system’s loops. It is installed on the Addressable Loop, powered by the Loop and monitors continuously the voltage levels and the signal’s integrity. The main supported function is to isolate a portion of the loop (between the two closer isolators) in the event of a shortcircuit. In case of two short circuit events, only the detectors before the first and after the second short circuit are powered. Repair of the short circuit condition brings the loop condition back to normal automatically (closed loop). Location of the short circuit position is achieved by reading the lost address detectors attached on the top of each isolator. We can have up to 4 additional detectors-devices connected and controlled on a single isolator output (A and B topology).