621 analogue addressable single input/output modules provide the interface to connect an electrically isolated dry-contact switched input to Numens 2-wire addressable fire detection control and indicating equipment. Up to 125 modules can be connected to each alarm zone loop.

A parallel resistive input filter allows multiple states to be monitored at the input. The states are converted to the loop communications protocol by the module, to enable them to be displayed on the control and indicating equipment.

The range includes a model with an integral isolator that protects other devices connected to the same transmission path. The isolator activates in the event of a short circuit in the loop wiring.