Replacing Smoke/CO detectors

So my project this past Saturday was to reevaluate the fire safety in our new house.

First up were the smoke detectors. We had seven FireX-brand smoke detectors hard-wired throughout the house: one in each of four bedrooms, one in the upstairs hallway, and one each on the first floor and in the basement. By being hard-wired into the house’s electrical circuits, they’re not operating on battery power most of the time (which means fewer times the batteries need to be changed) and they’re interconnected so if one alarm goes off, the rest of them will all go off too.

Some sources say you should replace your detectors every 10 years at a minimum, but some consumerists and FEMA say every 8-10 years. Our house was built in 2001, so the existing detectors were about eight years old. However, we have gas heat and water and no CO detectors, so now seemed like a good time to replace the smoke detectors and include some carbon monoxide detectors too.


If you have anything in your house that burns something–like natural gas, propane, heating oil, etc.–you need carbon monoxide detectors.  All of the fuels are hydrocarbons, which mean they are comprised of carbon and hydrogen atoms.

When hydrocarbons are burned, they mix with oxygen, producing heat along with two byproducts: H2O (water) and CO2 (carbon dioxide). However, if there’s insufficient oxygen present, the hydrocarbons don’t get completely converted to CO2 so you end up with CO: carbon monoxide. And that’ll kill you.


So I wanted to find some good smoke/CO combo detectors, and ideally I would have replaced them with FireX brand ones so I wouldn’t have to change the wiring harnesses cuz each brand seems to have their own harness to connect into the electrical. Since FireX got bought out, they’ve been hard to find in stores.

I ended up choosing Kidde’s smoke/CO combo detector, model KN-COSM-IB. They were readily found at both Home Depot and Lowes. (Pay no attention to the online price; they’re cheaper in the B&M store.) My local Lowes sold them for $43 apiece, but they also provided a contractor price, which came out to $36.55 each if you bought three or more. That’s an even better deal than using an acquired 10% off coupon. Since I was going to replace all seven of ours, I jumped on that deal.

Installation was a snap, even though I had to replace the wiring harness on all of them.  Even with just some basic electrical skills, it’s easy to swap out the harnesses. (Turn off the breaker first!) Unscrew three wire caps, remove the old harness, and then twist on the wires from the new harness and screw the caps back on. Took me about an hour to replace all seven.

As an additional installation note: I would recommend not pulling out the battery tab (to connect and activate the included 9V battery) until you are done installing all of them and have turned the AC power back on. After the unit receives power, it’ll start beeping and telling you (yes, it talks) to hit the test button and baseline the CO detector. By waiting, now you can test all of them at once (remember, they’re  all connected) by hitting the test button on one of them. Remember to stay at arm’s length, the alarm is LOUD. I waited until the test was done and then went back and pulled the battery tab on each one.

Kidde recommends that we replace these after seven years, and I think that figure is for the CO detector part of it. I printed out a few “Replace Feb 2016” labels on our Brother label maker and stuck them on all of them. All done!

One Reply to “Replacing Smoke/CO detectors”

  1. Nice review (best of all… adding some science!). a CO detector has been on my ‘to-do’ list since July 2007. 😉

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