The smoke detector is made with a controller and one or two sensors. The controller is designed to be powered with multiple voltages, 24vac, 120vac, and 220/240. The relay contacts in the controller provide connections for fire alarm systems, HVAC controls and other auxiliary functions. The smoke detector with two sensors does not differentiate which sensor signals an alarm. The sensor uses a process called differential sensing to prevent gradual environmental changes from causing a false alarm. A rapid change conditions, such as smoke from a fire, causes the sensor to trigger an alarm but dust and debris accumulated over time does not.

Air is introduced into the smoke detector’s sensing chamber through a sampling tube that extends into the HVAC duct and the sampled air exists through the exhaust tube back in to the duct system. When a sufficient amount of smoke is detected in the sensing chamber, the sensor signals an alarm state and the controller takes the appropriate action to shut down fan and blowers, send a signal to the fire alarm control panel if connected to it. These smoke detectors have an interconnect feature that allows up to fifteen smoke detectors to be connect to each other, so if one detector senses smoke it will trigger the other detectors to shut down the equipment there connected to.

The smoke detectors have LED’s to indicate conditions, such as power to the detector, trouble, a dirty sensor, or an alarm was triggered. These detectors are a great device that help to stop the distribution of smoke and probably toxic fumes in a building during a fire.