Many smoke alarms now come with sealed lithium-ion batteries designed to last for 10 years, and some building codes are moving toward requiring these in new construction. A 10-year battery eliminates the hassle of waking up in the middle of the night to the incessant chirping of a worn-out battery. It also reinforces the advice to replace alarms every 10 years. Once a 10-year battery fails, the whole device needs to be replaced. When detectors are about that old or older, replace them all at the same time. But if they are just a few years old and one keeps chirping even after you’ve replaced the backup battery or fails to sound when you press the test button, just replace that one.
Which replacement model you need depends partly on whether the existing devices are wired independently or are interconnected. If you aren’t sure what you have, press the test button on one. If all devices go off, they are interconnected, typically linked with a red or orange wire to carry a direct current signal in addition to regular alternating current wires for power. If only one sounds, they are wired independently.
If you have interconnected alarms, check the specifications to ensure you get a compatible replacement — or replace all the devices in your home with a single model or with ones listed as being mutually compatible. If the package isn’t clear, call the manufacturer’s consumer help line, which you can find on the company’s website. But if you have independently wired detectors, the replacement doesn’t need to match. It just needs to be a wired-in model.
Consumer Reports magazine, an advertising-free publication that regularly tests alarms, reported in a recent review that although it has found problems with carbon monoxide detectors, it has never found a smoke detector that failed its tests. But there are issues other than reliability to consider before you buy.
Modern detectors typically have a specially designed plug, which the industry calls a wiring harness, that links to house wiring. If you stick with the brand you have, the existing mounting bracket and plug will probably work. If you switch, you’ll probably need to install a new mounting bracket (typically included with new devices and easy to set up) and you may need an adapter plug (an extra expense).
Beyond that, there are performance issues to consider. One is whether to get a dual-sensing detector, with both a photoelectric eye to quickly detect smoke and an ionization sensor, often called a heat detector, to quickly detect flames. Both types of detectors sense both types of fires, but the speed of detection differs. So especially in a bedroom, a dual-sensing detector is best. You might want a photoelectric sensor in the kitchen, an ionization sensor in the garage, the ability to add a voice saying “Fire!” to alert a sleeping child, or a sensor with a strobe light for someone who is hard of hearing.
If you have independent sensors and a large multistory house, where interconnected detectors would be especially useful to ensure that everyone hears an alarm triggered in a distant room, you might want to spring for replacement detectors that interconnect via radio signal. They don’t depend on WiFi and will work even if the power is out. Examples include First Alert’s hard-wired smoke alarm with photoelectric sensor ($35.74 on Amazon) and Kidde’s 10-year worry-free hard-wired smoke detector with intelligent wire-free voice ($49.97 at Home Depot).
It’s also possible to incorporate “smart” home technology, so you can know something’s wrong even if you’re not home. Short of contracting with a home-security company or installing a DIY version, such as a SimpliSafe security system (simplisafe.com), you can get detectors that link to a cellphone. A wired-in Google Nest combination smoke and carbon monoxide detector is $114.99 on Amazon. There are also workarounds that add smartphone alerts to regular alarms. Kidde’s RemoteLync smart home monitor ($73.50) also listens for alarms and relays them to a cellphone using WiFi.
There are also some basics to consider before buying a replacement detector. It should have a label from a respected testing laboratory, such as UL. Check the manufacture date to ensure you get a replacement that is as fresh as possible. And look for a button that allows you to poke a broom handle at the device to get it to stop making noise when there is a false alarm.
Do you need to call in a pro to install new smoke detectors? In most cases, no, unless they are too high to reach from a ladder or stepstool that you feel comfortable using.
Get a stepstool or ladder, wear a headlamp if necessary, and grab a screwdriver and possibly wire strippers. Write the date on the back of the new detector. Turn off power to the circuit, and confirm it’s off by checking the LED light; use a noncontact voltage detector if you have an old detector that connects directly to the house wiring. Twist off the detector (look for an arrow showing the direction). If the mounting plate doesn’t work with your new detector, loosen the screws holding it in place just enough to twist off the old plate and install a new one. Retighten the screws.
Depending on your situation, you can then plug in the new detector, install an adapter plug or use wire nuts to connect the new detector to the house wiring after you first strip excess insulation from the ends of the detector wires. Tuck excess wiring into the ceiling box.
Before you twist the new detector into place against the backing plate, remove the tab that would keep the battery from working. Turn the power back on, and test the detector to ensure it’s working.
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