Types of Fire Alarms

Ionization Detectors

• Ionization detectors are the most common kinds of smoke detectors and fire alarms. Ionization detectors create a harmless level of ionizing radiation by using an electric current to create and release positively charged ions into the air. Smoke from a fire interferes with the constant electric current created by the ionization. When the electric current is inhibited, the alarm sounds to signify the presence of smoke or fire. Ionization detectors can be powered by small batteries that must be regularly checked and replaced. Ionization detectors are frequently the most reliable smoke detectors available to regular consumers, though they do not always respond to small or smoldering fires.

Photoelectric Detectors

• Photoelectric detectors and alarms use light-sensitive technology to detect the presence of smoke in a room. In photoelectric detectors, a beam of light is emitted from the detector in a straight line. A photoelectric sensor is arranged at an angle to the beam of light so that it can detect the degree of refraction of the beam. When smoke crosses in front of the beam of light, the light particles are scattered and refracted throughout the room. The light sensor detects the refraction and triggers an alarm. Photoelectric detectors respond better to smoldering fires and smoke than to large fires.

Thermal Detectors

• Thermal or heat detectors are not a common type of fire alarm because they do not react to smoke. Instead, thermal detectors are designed to respond once the temperature exceeds a set limit. Thermal detectors are not typically appropriate for household use because they do not respond until a fire has raised the temperature enough to trigger the alarm. Instead, thermal detectors are used in areas where smoke is consistently present, such as industrial buildings or commercial kitchens.