What are Dry Signal Contacts?

Dry contacts are also known as volt-free contacts or potential-free contacts are devices that switch to generate a signal but don’t have any power sources connected to them. They are either normally closed (NC) or normally open (NO).

Systems with dry contacts can be set to generate a signal when there is a change of state. An example would be a smoke or fire detector activating or door fitted with contacts, opening or closing.
Contacts such as these provide digital inputs (DI) which can be connected to a monitoring base unit. A signal is received; the monitoring device will record this and take a preset action.

Some monitoring base units also have digital outputs (DO). These can be used to provide a signal to a third-party system for it to take action. This is a form of machine logic, and an example would be to sound an alarm or flash a beacon if there is a physical security event such as a break-into a room or building.