What is a signal relay?

A relay is an electrically operated switch and in environment detectors, low current switching signal relays are used to indicate a change in operating state from ON to OFF or OFF to ON. A signal relay can be Normally Open (NO) or Normally Closed (NC). When a change in state is monitored, from NC to NO or NO to NC, an action can be taken. An example is a Smoke Alarm sensing smoke and changing the state of a relay as an audible and LED alarm is signalled. The relay can be monitored remotely by an environment monitor.