However, to become more consistent with international terminology manufacturers have recently changed the name to smoke alarms. A smoke alarm is the most common and most visible fire safety device in homes today. When installed, used and maintained property they greatly increase your chances of surviving a fire. But, an alarming number of these devices no longer function properly or fail to work at all. There are two basic types of detectors, photoelectric and ionization.
Photoelectric units use a beam of light and a light sensor to detect smoke.
The light is constantly on but is not pointed directly at the sensor. When smoke enters the detector light is reflected off the particles of smoke and onto the sensor. This sounds the alarm. Photoelectric detectors respond faster to the large smoke particles created by smoldering fires. Ionization units measure the electrical current in the air between positive and negative charges of ions.