How Does A Smoke Detector Work?

How does a smoke detector work? Smoke detectors are great inventions, and they are not only extremely useful, but they are also easily accessible. They are inexpensive and available in most stores, but most importantly, they save thousands of lives each year. But, for as valuable as smoke detectors are, not many people understand how they work.

In their most basic form, all smoke detectors work the same. There is some kind of sensing mechanism that recognizes the smoke, and then there is an alarm that reacts to that smoke. However, there are two specific types of smoke detectors that each complete this process in different ways.

Understanding the different types of smoke detectors can help you make a more informed decision about what you buy, and knowing where to place your smoke detectors and how to maintain them will help keep you as safe as possible.

Two Types of Smoke Detectors

There are two primary types of smoke detectors: an ionization detector and a photoelectric detector. The main reason that there are different types of smoke detectors is that there are different types of fires, so while the purpose remains the same, these smoke detectors will do their detecting in different ways.

You can think of the difference between the two smoke detectors like the difference between your eyes and your nose. One detector uses light and sensors, while the other uses chemistry to detect a change.

About the Photoelectric Detector

One type of smoke detector is the photoelectric detector. To put it simply, the photoelectric device uses a photoelectric sensor and a light source to detect smoke. There will be a light beam inside of the smoke detector chamber, and when smoke enters the chamber and crosses paths with the light beam, the light is scattered. The sensor picks up the scattering and in turn triggers the alarm.

Inside of the smoke detector chamber is a device called a photocell, which generates electricity when light falls on it. Until smoke falls upon the light, the light beam isn’t able to reach the photocell, so it’s the smoke that causes light to scatter and trigger the circuit that sets off the alarm.

While there are other particles that could scatter the light, this really isn’t an issue. Since smoke rises, it will rise into the smoke detector, which is placed on your ceiling, so this type of detector works well.

About the Ionization Detector

On the other hand, the ionization detector works entirely differently, and generally, ionization detectors are less expensive than other types. The ionization detector uses a kind of chemistry to recognize molecules that aren’t supposed to be there, which in almost all cases will be smoke.

Inside of the ionization detector is something called an ionization chamber, and inside of this chamber is a chemical element called americium. The americium spits out alpha particles that leak into the ionization chamber and interact with the air molecules, creating both positively-charged ions and negatively-charged electrons that are in constant movement. They travel between two electrodes and create an electric current.

As long as these particles are in motion, the alarm won’t sound, but when smoke infiltrates the ionization chamber, things get clogged. The smoke particles attach to the ions in the chamber, slowing them down and cutting off the electric current. The circuit in the smoke detector will notice this change and react sounding the alarm.

Which Is Better?

Deciding which smoke detector is better is tricky because it really depends on the origin of the fire. Both smoke detectors are effective, but ionization detectors are more responsive to flaming fires such as a flaming window curtain, whereas photoelectric detectors are most effective when it comes to smoldering fires that lack prominent flames.

The one you choose could depend on your habits. For example, a lit cigarette on a couch would produce a smoldering fire, so if you smoke indoors, you might choose a photoelectric detector. On the other hand, if you light a lot of candles, an ionization detector might be better.

Dual-Sensor Devices

Of course, there is nothing stopping you from buying both types of smoke detectors if it’s in the budget. You can feel free to place an ionization detector directly next to a photoelectric detector for maximum peace of mind. Otherwise, you might consider a dual-sensor device.

Dual-sensor devices contain both ionization technology and photoelectric sensors, so you wouldn’t have to worry about which type is best for your home, and you wouldn’t have to buy two different smoke detectors. For obvious reasons, these are more expensive, but if your budget will allow for it, a dual-sensor detector could be the better option.

How Are They Powered?

In terms of power source, there are also two main types of smoke detectors. Some smoke detectors are battery-powered, meaning you will have to replace the batteries every so often if you want your smoke detector to function. Alternatively, your home’s electrical system will power other types of smoke detectors, and these will be hardwired into your home.

Usually, the hardwired smoke detectors are equipped with backup batteries anyway, but regardless of power source, it’s important that you are checking your smoke detectors regularly. If you have a battery-powered smoke detector, it may be wise to keep some batteries around the house so that you can change them out whenever you need to.

The Importance of Checking Your Smoke Detectors Regularly

A lot of people wouldn’t be able to say with confidence that their smoke detectors even work. That is until they’re fanning at the fire alarm after a cooking mishap sends smoke up to the ceiling. But, in general, fires are rare, so it’s not uncommon for homeowners or business owners to go years without ever hearing their smoke detectors go off. For that reason, it’s important that you are always checking.

The U.S. Fire Administration recommends checking your smoke alarm once a month, and there will usually be a test button on the device itself. If your smoke alarms don’t work, they are essentially useless and won’t be of any help in the event of an actual fire. If you don’t check your smoke detector, and you are a good cook, you may not find out until it’s too late.

How to Check Your Smoke Detector

Smoke detectors will have a test button that you can press, and this will tell you whether or not the smoke detector is working. However, there are a couple of things you will want to do in addition to pressing the button.

First, you will want to alert your family or your employees that you are testing the equipment. A smoke detector alarm is high pitched and possibly frightening to those who aren’t prepared. With that in mind, you might want to prepare yourself since you will be the closest. Lastly, you want to station a family member at the far end of the house to ensure that the smoke detector alarm can still be heard.

For battery powered smoke detectors, keep in mind that your smoke detector might sound without anybody touching it, and this can mean that your batteries are dying. Some batteries will last a long time, but it’s still better to be safe by checking your batteries every once in a while.

Where to Install Smoke Detectors

A smoke alarm that cannot be heard everywhere in the house is only slightly more useful than one that doesn’t work at all, and depending on the size of your home, you may need more than one to achieve optimal safety.

When you are installing smoke detectors, you will want to keep in mind the number of floors in your home as well as the number of bedrooms. You will definitely want at least one smoke detector per floor of the home, but the Nation Fire Protection Agency also requires one smoke detector for the inside of every bedroom, as well as one for outside each sleeping area. With that in mind, a 2-story, 3-bedroom home would have a minimum of 5 smoke alarms.

Different states will have different standards and regulations, and not only is this a safety measure, but in some cases, especially for businesses, smoke alarms are required by law. Working smoke detectors are also required for a lot of insurance policies.

Interconnected Smoke Alarms

Interconnected smoke alarms don’t function any differently than a stand alone smoke detector, but they are safer.

When your smoke alarms are interconnected, they react to each other. If one smoke alarm detects smoke and sounds the alarm, the rest of the detectors in the building will sound as well. This ensures that everybody in the building, regardless of location, can react in the event of a fire.

Smoke detectors that are interconnected will typically have to be hardwired, but the extra work will certainly be worth it, especially if you live in a large home. For greater protection, you can also get CO detectors that are built into your smoke detectors, and this way you will be ready for anything.