How Does a Smoke Detector Work?

Purchasing a smoke detector is really a simple affair. There are two types of smoke detectors, and both work well.

  1. IONIZATION detectors use an electrical charge. In this unit, there are two plates that are a small distance apart, and each carries an opposite charge. One is negative, and the other is positive. The plates are far enough apart to not short out. When smoke enters the area between the plates, it picks up a charge. When the smoke density gets to the correct point, it shorts between the plates, and the alarm is sounded.
  2. PHOTOCELL  versions are the ones with the pretty little red LED light. This light beam is normally not directed at the receivers in the alarm which pick up the beam. However, when smoke enters this alarm, the light beam is scattered in such a way that it hits the receivers and triggers the alarm.

An ionization detector seems to work faster in a fire with a large flame, but the photocell triggers first most of the time in a smoldering fire. In a large building, it is recommended that you install both types of alarms. Keep in mind that both types do well in all fires and the differences in reaction time are just seconds.

According to the NFPA72, each sleeping area should have a detector. There should be one in the kitchen. If the home is more than one level, there should be one on each level.

In new homes, these detectors are required to be hard-wired to prevent tampering.

Another factor to consider is that the installed alarms must be loud enough to be heard in various rooms with all doors closed and over any background noise.

Any detector mounted within 20 feet of a cooking appliance must be photoelectric OR have a silence button. If not, the head must be removable. We have all heard the jokes about the little boy who hears the smoke alarm and runs to tell Daddy that dinner is ready!

Your detectors should be interconnected. This means that when one sounds, they all will, giving better odds that they will be heard.

Never paint over your detectors and be sure to check them monthly. Many find it helpful to put a reminder in their phones on a recurring basis. If your home has battery operated versions, change the batteries at least two times per year. It has become common for fire departments to remind everyone when the time changes in the spring and fall.

Smoke detectors are one component of a complete fire safety system. You should also have fire extinguishers in strategic locations, near where they may be needed. Some types of homes have sprinklers installed as well.

If you have questions about your current home’s system, or have purchased an older home with no alarms or inadequate coverage, call us! Smith Electric & Associates is in Mobile, Alabama. We are licensed to operate in Alabama, Mississippi, Florida, and Georgia and have been proudly serving the Gulf Coast since 1992. Call us for 24-hour emergency service at 251-471-4723! Visit us online at and connect with us on Facebook and Twitter!