In conventional systems, detectors are hard wired into a circuit
or zone. They signal a fire condition to a control panel by
changing from a high to low impedance. The panel detects this
impedance change by current monitoring and identifies the zone.
Individual detectors cannot be identified. In two-wire conventional
systems, fire detection and alarm products are connected to the
same pair of supply wires, making installation quicker, less
expensive and more flexible than traditional four wire systems.
Two-wire systems are particularly well suited for small to medium