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Smoke Detectors

Smoke Detectors
(for Carbon monoxide detectors, click here.)
Important Information:  Smoke detector manufacturers recommend replacing smoke detectors at least every 10 years. Research shows 30% of detectors fail after 10 years, 50% after 15 years!

Years in service
Failure rate
1 year
10 years
15 years
30 years

 (Read about CO detector replacement (5-7 years) by clicking here.) 
More information is available at NFPA (National Fire Prevention Assoc.) web site.   
An excerpt:  (NFPA 72 Sectdion 10.4.7, emphasis added)

10.4.7 Replacement of Smoke Alarms in One- and Two Family Dwellings. Unless otherwise recommended by the manufacturer's published instructions, single- and multiple-stations smoke alarms installed in one- and two-family dwellings shall be replaced when they fail to respond to operability tests, but shall not remain in service longer than 10 years from the date of manufacture.

Or read the FAQs at Kidde.

We're used to getting calls occasionally to replace defective smoke detectors, now we know why.  This should become a planned maintenance item.  How old is your house and your detectors?   The newer designs have a latching relay (to tell you which unit triggered the alarm) and a temporary hush feature (for a kitchen cooking mistake) that automatically reactivates itself after 8 minutes.

What type of detector do you have: 120 volt, or low voltage?

120 volt (newer)
120 volt (older)
low voltage
(security system)

120 volt timer newer

120 volt timer older

low voltage smoke detector

Call us
Call us
Call your
alarm company

If you also have a (low voltage) burglar alarm/smoke detector system, in most cases, you still need the 120 volt interconnected detectors we're discussing here. The reasoning is that a homeowner could easily choose to not use their alarm system and therefore not have a functioning smoke detectors in the home.

General Information
Enjoying life lately?  How about ensuring that you and your family are around to enjoy more?  Reports have shown that over half of the smoke detectors in homes are not functioning properly.  Often, it's as simple as a bad battery, or sometimes, people have even removed the battery!

There are 3 basic types of smoke detector installations:

  1. Battery only (9 volt) which are simply attached to the ceiling.  These are usually found in homes built before 1980 or so.

  2. 'Hard-wired' 120 volt smoke detectors.  Homes built after 1980.  These are wired similarly to lights, etc., but they are also interconnected so that if 1 detector senses smoke, all the detectors go off.  This is so you hear the alarm even if you're in another part of the house.  Almost all of these units now also have a volt battery back-up power.  In case of a power outage, when people may bring out candles, it's nice to know the detectors will still be functioning.

  3. 'Hard-wired' low voltage smoke detectors.  (Some homes with security systems.)  These are part of the household burglar alarm system.  The battery back-up of the alarm system provides power in case the electricity goes out.  These systems are best maintained by your alarm company. (Note that these alarms alone do not satisfy the residential fire code (see not above).

If you have 120 volt powered smoke detectors, now would be a good time to find out what circuit they are on and label it.  You don't want to try to figure out what breaker it is if you get a false alarm in the middle of the night.  Have someone watch the power LED while you flip breakers off until the LED goes out.

What do you do if your smoke detector system goes off?
First, check to be sure everyone is safe and there is no fire.  Sounds simple but you don't want to assume that it's a false alarm.  If it is a false alarm:

  • For battery or single detectors (non-interconnected), you can try to clear the alarm by blowing or vacuuming around the detector in case dust is causing a problem.  Your last resort is to remove/disconnect the power or battery.

  • For interconnected smoke detectors, you need to determine which detector is causing the alarm and disconnect it.

    • Different models of smoke detectors have different methods of indicating which detector is initiating the alarm and thereby activating all the others.  The key is the red LED indicator lights.  On some systems, the problem detector will show no red LED while the others all have steady on LEDs or blinking LEDs.  Some systems are the opposite.  What do you do for your situation?  The answer is simple;  "it's odd man out."  Simply look at the detectors and see which one detector has a different LED pattern than the others.  The one that is different is the one that needs to be replaced.

    • If you know what circuit breaker powers the detectors, turn the breaker off.  The battery back-up will still keep the detectors alarming.

    • Then, usually a simple counter clockwise twist of the smoke detector will allow you to detach the unit from its mounting plate.  Then disconnect the plug connector on the back.  Be careful if the circuit breaker is not off since you have 120 power at the plug connector.  At this point, the other detectors should stop alarming and be silent.  If not, you haven't found the problem detector.

    • Finally, remove the 9 volt battery and the problem detector should stop sounding.

  • Low voltage detectors are wired as a zone.  You should be able to deactivate or by-pass the zone.  You will have to check your manual or alarm company for more information.

Helpful Hints:

  • Test your system occasionally.  For interconnected units, it helps to have someone else to tell you if the other detectors also are triggered when you press the test button.  Usually, they start 1 or 2 seconds after the first one.  Be sure to press the test button on each unit.  Even you've had a lightning strike or surge, be sure to test the detectors to verify their electronics have not been damaged.  See Surges below and Lightning above.

  • Replace all the batteries every 6 months.  An occasional chirp sound indicates low battery.  Be sure the battery back-up of your smoke detector system is working properly.  (Usually, the detectors have an indicator light that blinks every 30 seconds to show the battery is still good.  Different brands and models vary in how they show power and battery.)

  • If you're getting an occasional chirp and you've changed all the batteries, also check your carbon monoxide detectors to see if their batteries need replacement.  Red more on CO detectors, click here.

  • If your detectors are over 10 years old, it's important to replace all of them.  See the UPDATE at the beginning of this Smoke Detector section.  New detectors are 120 volt with battery backup, can indicate which unit is triggering the alarm, and sometimes have a temporary shut-off for cases of nuisance alarms.

  • If you need more information about your detector:

  • Smoke detectors work as a system. You can't mix different brands in a system, they have compatible electronics.

  • Identify and label the circuit breaker for the smoke detectors.  This has 2 benefits:

    1. You can shut the circuit off and test the battery back-up.  Press the test buttons on each unit.

    2. If the unit goes bad in the middle of the night and triggers all the detectors, you'll be glad you know which breaker controls them.  Although the battery will still control them, you are one step closer to quieting them.

  • Notes: (BOCA - Building Officials and Code Administrators), (NFPA - National Fire Protection Association)
    1984  BOCA requires 1 detector per floor

    1988  BOCA requires interconnected detectors
    1989 NFPA 74   requires interconnected detectors in new construction, 1 per floor
    1993 NFPA 72   requires interconnected detectors in new construction, 1 per floor/1 within 10 feet of any bedroom, 1 in each bedroom
    1999 NFPA 72   requires smoke detector replacement after 10 years maximum