We have hardwired (connected to household electric) smoke alarms, so the batteries only get drawn upon directly when the power is out. I change those once a year in spring at the daylight savings shift, instead of every six months which is the rate recommended for battery operated alarms. 9V batteries taken out still have plenty of charge in them, but replacements are cheap enough I just don't want to take any chances with my family's safety in deviating from a set replacement schedule. I respond to alot of fires for the Red Cross, and in almost every instance its a smoke alarm that alerts people to the fire and that gives them time to get out safely.

Worse case, if we had a long duration power outage the battery backup would be drawn upon, so I would just change my smoke alarm batteries when the power comes back on.

Here's a related follow-on question--Has anyone ever had a 9V battery leak?

Perhaps the 6-month rule came about at a time when batteries were less reliable, and 6-month replacements made more sense? I've never seen a leaking 9V, and with the availability of lithium 9V cells now, you could go many years without changing those puppies.

I have fond memories of a 9V-powered transistor radio from Radio Shack when I was a child. It came in many colors, I recall. They don't make 9V radios anymore, it seems, but that would've been a good way to use up those cells from the smoke detector.

Yes. However it was many years ago. The only gear I have that runs on 9V batteries now is my cable tracer set, and I haven't used that for a couple of years.

I'll second the recommendation for the PALight/Safety-Light flashlights. 9volt is a bit of an oddball battery, and it wouldn't have been at the top of my list for most purposes, but it works great with these lights.

The thing I like best about them is their extremely low "always on" level - great for a nightstand light. You don't notice that they're on when there's a light on in the room, and when the lights are all out, it's enough light to easily find the flashlight on the table top without disturbing your night vision or being an annoying source of light when you're trying to sleep. Then you can use the light as needed. Even on its highest setting, it's not what you'd call a terribly powerful light (LED technology has really leaped forward from when these lights first came out). But they're very useful lights.

One tip I got from CPF back when I first got my PALights - they come with a plastic lens that focuses the beam a bit more tightly than I find optimally useful - the tip was to pry out the lens and reverse it, so that it's got a broader beam. I prefer my lights that way - it might not be everyone's preference.

Ah, that's a great tip. I had not thought of that--turning that focusing optic into a spreading optic.

That optic is my primary reason for never getting a Survival Light or PALight back when they first came out years back--the beam is a distinct circle with a sharp cut-off, so you suffer from that "follow the bouncing ball effect" because you can only see what is within that circle. To be fair, that was quite common among many lights back then, when LEDs were pretty weak and you had to do things like use a lens to concentrate all that light into a smaller beam. We've certainly a long way from then in a short time.

I've always wondered how necessary the 6-month replacement rule is.

It reminds me of vehicle maintenance suggestions; cars all used to say the oil had to be changed every 3 months or 5,000 km. I always thought that was excessive, and newer vehicles with oil life monitors seem to be proving me right; according to GM's info on cars with their oil life monitoring system, "[m]ost GM vehicles average 13,500 km between oil changes." That's quite a difference.

It makes me wonder if we are being wasteful in changing all those batteries on a 6 month schedule (although searching around I see quite a few organizations recommending annual battery changes now - example).

As a side note, some manufacturers are now selling 10 year smoke detector models with lithium batteries installed; they say the life of the unit is the life of the battery so you just replace the whole unit at the end of 10 years.

Sorry to continue this tangent, but that's an important point--smoke detectors lose sensitivity for a number reasons over time, so most should be replaced at the 10 year mark (at least the ionization type). However, how many of us reading this post have smoke detectors that are more than 10 years old? Quite a few, I'm sure.

I just checked--I do have two units that are way past their prime. Something to remedy this holiday season, especially before any Christmas tree goes up.

I've read that smoke detectors should also be vacuumed to remove dust that can reduce sensitivity, but that's something I've never done.

Skylite

Starlite

9v batteries are actually comprised of 6 AAAA batteries inside a rectangular casing. You can have a 9v battery where the internal AAAA batteries are leaking, but fail to permeate the metallic casing. Ever have a 9v that looks overly fat/distended? Yup, it's leaking internally.

I suppose that's why they recommend such frequent replacement. You could have a failure inside the battery and not even notice it because of the battery's external case shielding the problem.

Interestingly, all the new battery operated smoke detectors I've seen now use AA batteries. Thankfully, I gave up on battery powered smoke and CO detectors years ago and just had them all hard wired into the alarm system. Now I've only got one battery to change...the backup battery down the basement....which supposedly has a 10 year lifespan (though I change it out every 5 or so).

I've always wondered how necessary the 6-month replacement rule is.

I suspect that part of the point is to get people into the habit of keeping that vital piece of equipment working. Too many people either forget about them, and many don't even have alarms. A dead battery is as bad as not having an alarm at all.

Does any know how much power the alarm going off drains? A few kitchen issues, humidity from the shower, grumpy toaster..... How long is the battery life if the unit is doing more than just waiting?