Which detector is described as using a beam of light across a room to detect smoke in large spaces?

• A. Ultraviolet detector
• B. Ionization detector
• C. Projected beam detector
• D. Heat detector

Answer: (C)

In large spaces, you detect smoke by monitoring a light path across the room. A projected beam detector does just that: an emitter sends a beam of light (often infrared) to a receiver across the space. When smoke enters the beam, the light is scattered or blocked enough to trigger the alarm. This design covers wide areas like warehouses or long hallways with a single detector setup, rather than needing many small point detectors.

Ultraviolet detectors focus on detecting flame UV radiation, not smoke in a room. Ionization detectors sense smoke by how particles affect an ionized chamber, not by a light beam across a space. Heat detectors respond to temperature changes, not smoke.