"The FW859 In-Suite Isolator module is designed for residential and hospitality-based applications. The In-Suite Isolator can detect a short circuit condition on a Class A circuit that covers a suite by electrically isolating the wiring."
The module FW859 Supervised In Suite Isolator Module is designed for installations where disconnection of, or damage to an in-suite audible device will not interfere with the ability of audible devices in other dwelling units, public corridors, or suites to sound on an alarm. The FW859 mounts in a 4” square electrical box. The FW859 provides two supervised isolator outputs. Under this configuration, if the insuite audible device has an open circuit, the fire control panel will indicate zone trouble. It is a UL/ULC listed product according to UL864 and ULC-S527 for Fire Protective Signaling Systems for indoor use."