A smoke detector has one job, which is to notice smoke early and make enough noise to get people moving. Inside, it’s a sensor and a horn, running on a battery or on the building’s power with a battery backup. A photoelectric detector senses smoke with light.
The idea behind it
You’ve probably walked into a store where a chime goes off as you come through the door. There’s a light on one side of the doorway and a sensor on the other, and when you walk through, you block the beam. You could catch smoke the same way, but it would take smoke thick enough to block the whole beam, and by then you’d already know there was a fire. So a photoelectric smoke detector uses the light a different way.
What’s inside
Inside the detector is a small, dark chamber with a light, usually an LED, and a light sensor. They’re set at an angle to each other, so the light shoots across the chamber and misses the sensor. With clean air in there, the sensor sees nothing.
What happens when smoke gets in
When smoke drifts in, the particles scatter the light, and some of it bounces onto the sensor. Once enough light hits it, the detector sets off the horn. It doesn’t take thick smoke, just enough to bounce the light.
What it’s best at
Photoelectric detectors are quick on smoldering fires, the slow kind that smoke for a long time before they ever flame up, like a cigarette dropped in a couch or a mattress that’s smoldering. Those fires put out bigger smoke particles that scatter light well. On a fast, flaming fire with very fine smoke, an ionization detector usually reacts a little sooner. That’s why many buildings use both types, or a dual-sensor detector that does both. Photoelectric detectors are also less likely to go off from a little cooking smoke, so they’re often the better pick near a kitchen.
Keeping them working
Dust and bugs can get into the chamber and set off false alarms, so it helps to vacuum around the vents now and then. Test it with the button once a month. If it takes a regular battery, change it once a year, and replace the detector when it hits 10 years. The date is on the back.
In a business
Most businesses have their smoke detectors wired to a fire alarm panel, so when one trips, the alarm goes off through the whole building. We install fire alarm systems, test the full system every year, and offer 24/7 monitoring. We put smoke detectors in with home security systems too. Call 1-800-348-9604 if you want somebody to look at what you’ve got.