Horns and sirens, also known as “sounders”, are tone generators that output an audible signal when a voltage is applied to their input power terminals. Sounders are self-generating – meaning that the tones are pre-programmed into their circuitry and the sound is simply emitted when power is supplied.

Sounders are widely used for generating evacuation alarms in the event of fire, toxic gas leak, or chemical spill. Other applications for sounders include machinery start-up alarms, back-up warning systems, process upset signals, heavy equipment movement, moving roof systems, crane movement, and movement of doors, gates, and barriers.

Sounders typically generate a variety of tones that can be user-selected. Some units are capable of delivering multiple tone stages. For example, one tone stage may signal evacuation, while a secondary tone stage may signal “all clear” or OK to return.