The Kidde SL177i is a 120VAC wire in unit that provides a visual warning when part of an interconnected system. This unit can be directly interconnected with Kidde smoke alarms, heat alarms and carbon monoxide alarms (a maximum of 24 devices of which 18 can by initiating). When triggered by a smoke alarm or heat alarm, it will produce a steady flash warning. When triggered by a carbon monoxide alarm it will produce an intermittent flash warning. The SL177i has a 5 year limited warranty and is UL Listed