What is one of the two types of smoke alarms/detectors?

• A. Photoelectric
• B. Heat detector
• C. Ionization
• D. Carbon monoxide detector

Answer: (C)

Smoke alarms are categorized by how they sense fire: ionization or photoelectric. Ionization detectors use a small amount of radioactive material to create ionized air in a sensing chamber; when smoke enters, the ion flow is disrupted and the alarm sounds. They’re known for responding quickly to flaming fires. The other main type uses a light beam and detects smoke by scattering that light; this type tends to respond well to smoldering fires. So ionization is one of the two primary smoke alarm types. The remaining options refer to different devices (heat detectors respond to heat, carbon monoxide detectors sense CO) or to the other smoke alarm type, which would be a separate correct choice if asked for another example.