Selecting a Smoke Detector

Whether you are looking to add or replace smoke detectors there are  4 variables you should consider. 

  1. Sensor Type - Ionization,  photo electric or dual sensor
  2. Power Source - 110 VAC Hardwired, Battery,  Low volt wired
  3. Interconnected or not
  4. Single Detector or combo unit with CO Detection


Sensor Type - Ionization, Photoelectric or combo

The first factor is the sensing type, ionization or photoelectric. Ionization are cheaper, but more sensitive to flaming fires and hot invisible particles from a high heat source. These are the detectors that go off when you open the oven door or the toast pops up. You may see no smoke, but excited electrons and other particles are flowing fast and furiously. Ionization detectors are best for sensing flaming fires.  There down side is you get tired of them going off so you pull them down. They don’t work when you take them down. Ionization are good detectors,  you just need to be smart in where you locate them.

Photoelectric smoke detectors use a small light source on the edge of a chamber. Surrounding the chamber are light sensor(s). The sensor can’t directly receive light from the light source but when particles flow into the chamber, light bounces off the particles and into the sensors. The unit goes into alarm.  This type of sensor is better for detecting smoldering fires where smoke may build up slowly.

Both types are very common on the market. You can buy combo units that use  both sensing types. In some jurisdictions you may be require to only use ionization / photoelectric combo units. Check with your local fire department (don’t call 911) or building codes department.   To the best of my knowledge, the Photoelectric type is always used on low voltage smoke detectors that are part of a fire / security system.

Power Source - 110 VAC Hardwired, Battery,  Low volt wired

There are three ways you can power smoke detectors. The first is 110 VAC (common called ”line powered”) which was install when the home was built or remodeled. If you remove a smoke detector and you see black and white wires (such as those used for home wiring by electricians)  you have a 110 smoke detector. You will also probably see a red or yellow wire as well. This third wire is the interconnect wire (more on that in the next section).

Low volt smoke detectors will always be wired to a control panel, unless they are wireless. In both cases there will be a keypad someplace, possibly right next to the panel if the system is only used for fire and not burglary. If you open the panel, there will be battery inside. These batteries need to be replaced every five years and should be checked every year by a professional for proper charge and discharge. If you cannot find a keypad or panel and you still think your smoke detectors are a low volt type, please contact a security professional. If you remove a wired low volt smoke detector from a functional system, your keypad will beep or otherwise inform of a problem. ALL low volt wired smoke detectors must be in place for the system to operate. If you remove a wireless smoke detector from a low volt system, the keypad will still beep to inform you someone tampered with the detector, but the system will still function.

The last method of powering a smoke detector is of course, batteries. Battery powered units have some along way recently. You can buy detectors with a sealed lithium battery that last ten years, which is the life span of most units anyway.  

Interconnected or not

Interconnected smoke detectors are just as it sounds. When one goes off they all go off .

Almost always, all 110 hardwired smoke detectors are interconnected by a third wire, usually yellow, orange or red, that comes from the detectors. Using a three conductor with ground romex wire, these trigger outputs are all tied together.  You should always verify your system if you are in a new home or apartment. Test one detector and verify all the others went off as well. You may need to do this test a few times on a large home.

Not all low volt smoke detectors are interconnected.  Low volt detectors come with or without an internal siren. Units with internal sirens should all make noise when one unit goes off, but if they don’t have internal sirens, then you should have a separate stand-alone siren on each floor of the home.  If you have not had a security professional test you system and verify all detectors operate and each can trigger an alarm, please contact them. NEVER ASSUME THEY WORK BECAUSE YOUR WHERE TOLD THEY DID BY SOMEONE ELSE.

For homes with non-interconnected line voltage detectors or battery powered units, First Alert make a complete line of smoke detectors and CO detectors that link together wirelessly. This allows you to create a linked smoke detector system using a mix of hardwired and battery powered detectors. The First Alert Detectors are NOT for low volt systems which are part of a security system. 

Smoke / CO Detector

Just like it sounds a Smoke/CO detector combines both sensors into a single unit. Carbon Monoxide poisoning results in over 400 deaths a year ( CO detector codes vary from state to state but in general you should have a CO detector on every floor if your home has an attached garage or has any fossil fuel or wood burning appliance. This would include gas or wood burning  stove, furnace, fire place or boiler.  Even if your home does not meet these requirements I still recommend installing at least one CO detector on each floor of your home and in your bedroom hallway. Almost every year you hear a story of how someone or entire family died because someone thought it would be a good idea to use a BBQ to heat a home or some other bad idea.  A CO detector can be a good investment in protecting your family from bad ideas.

When you are evaluating your smoke detector system you should always consider including CO detectors in those areas either required by code and where they just make sense.  If using the same brand you can mix Smoke Detectors with Smoke/Co Detectors to build a complete system that will protect your family. You can mix brands of detectors if they are stand alone units, but if linked or interconnected you should always use the same brand and verify the models are compatible with each other.

Always follow manufacturer guidelines for placement and installation.