Changing batteries in hard wired smoke detectors

Paddy · Jan 4, 2016

How often to you change your batteries in your hard wired smoke detectors? I assume, but not sure, that if the power is on, the detector does not draw power from the battery. If that is the case, then the battery life is the shelf life of the battery.

What made me think of this was when I removed the old batteries I noticed the shelf life dates were the same as what I was replacing them with. Guess they came from the same box, I don't think I have any other equipment I use 9 V batteries in. Recently bought a new pack of batteries and saw they had a shelf life extending out 4-5 years.

Not intending for this to be a discussion of, "if you value your family you would change them xx times a year". I have 11 smoke detectors now, 5 more to go into basement and garage. I also have a sprinkler system where every room has at least one head, some 4.

DFB · Jan 4, 2016

Mine have a low battery warning "chirp"

Never fails to start in the middle of the night either

MarkF48 · Jan 4, 2016

If not changing out the batteries routinely, perhaps just taking a look at the battery to check for any evidence of leakage which would eventually ruin the battery compartment and a quick voltage test with a digital meter (some meters can do a load test on batteries).

k0ua · Jan 4, 2016

DFB said:
Mine have a low battery warning "chirp"

Never fails to start in the middle of the night either

About 2:00 AM for most of mine...

Carl_NH · Jan 4, 2016

Recently some started chirping so replaced the battery, still chirped - I believe there is like a 7-10 year clock built into the detectors to signal replacement.

Same thing happened to the plug in CO Monitor - had to replace it and on the fine print it says "unit will chirp after 7 years indicating it is time to replace"

charlz · Jan 4, 2016

I have always assumed that they do a battery test every few minutes. They will start chirping in the middle of the night, typically Fall/Winter nights, when the house is coldest and thus the battery output is lowest. They can/will then stop as the house warms up later in the morning and start again the next night. If that is indeed the case then the battery being tested over and over again will eventually draw it down. I don't think just some calendar interval would be advisable/allowed in a safety device.

rhunt · Jan 4, 2016

I change the batteries once a year, always on July 4th, easy to remember. The directions that come with the hardwired smoke detectors recommend once per year.

s219 · Jan 4, 2016

DFB said:
Mine have a low battery warning "chirp"

Never fails to start in the middle of the night either

Ours too. I have never ever heard them chirp in the middle of the day. Always seems to be at like 2AM.

Our new house has smoke detectors with a built-in lithium-ion battery that is good for 10 years. One of them, in my daughter's room, kept going off (at 2AM), and we determined it was the use of baby powder in that room that was doing it.

On top of that, I later discovered that one of the wires to the unit was not tight (wire nut was loose) so every time I pulled it out to silence it, the wire kept working loose. Finally it would not stop chirping, so I took it outside (again at 2AM) and beat the crap out of it with a hammer. The lithium-ion battery really shot off some sparks. Replaced it with a regular 9V battery unit, which is when I discovered one of the wires had worked loose, which probably exacerbated problems with the old detector (they will chirp when no AC power and the internal battery runs down).

What really bothered me is that when that smoke detector would go off, it would trigger the glass-break sensor on our security alarm. So we'd be awakened at 2AM by a smoke detector, and then a few seconds later the security alarm would go off. It has an independent fire/smoke detection system, so the first time it happened I was sure there had to be a fire, what with two independent types of alarms going off. What a way to wake up at 2AM....

Coyote machine · Jan 4, 2016

The 7-10 year replacement chirp is NOT the same as the replace battery chirp. When the 7-10 year one goes off the useful life of the detector is DONE and needs to be replaced. I thought they were closer to 5 years lifespan- but not sure on that detail.....
Also vacumm out cobwebs etc., when changing the battery. If doing painting/sanding in the area of a detector put a plastic bag over them until the entire room is dust free.