How often to change batteries in electric powered smoke detectors?

Bought a house 6 months ago with all electric powered smoke detectors that have a battery back-up. Sure enough, 3 AM, one starts chirping every 30 seconds. Really pissed off the dog!
Seven detectors, so I changed the batteries in all of them, because the dog said she didn't want another 3 AM wakeup call.
No manual, just wondering how long they last when they are AC wired? I know battery only, they recommend once or twice a year, but what about AC powered? I would think several years, no?
Thanks,
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I've found it's still once a year with the AC wired units. It's not worth the lost sleep trying to go longer.
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<stuff snipped>

That's when it's coldest part of the day and dying alkaline batteries are susceptible to the cold. I just opened up a pack of Ray-o-vac 9V I got from Fry's. One was 3V and the three others were well under 9V. Date 2013. They're getting a phone call Monday. The 9V batteries are expensive enough to begin with, but I having to buy them twice? No deal.
-- Bobby G.
-- Bobby G.
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Well, that's because batteries degrade faster when it's hot.

It's always something. Think of it as Global Current Change.

Now you have.
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wrote:

are
That's actually part of why they die more in fall. They've been baking all summer and when the first cool-down comes, they pass rapidly into old age. It's doesn't have to get very cool to push an almost dead, heat-baked battery into the dead zone.

Not if those neutrinos really did go faster than the speed of light. I suspect another cold fusion experiment.
http://www.forbes.com/feeds/ap/2011/09/24/science-eu-breaking-light-speed_8698457.html
-- Bobby G.
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Slight temperature drop really IS the answer. It's like the old joke, I don't have to outrun the bear, I just have to outrun you. I'm an obsessive about recording temperatures and home automation so I've seen this happen. It cools down enough at night in the fall to drop the battery voltage just enough to trigger the beep alarm.
You'll see "early morning beeping" more in the fall than the spring because the overall outdoor temps drop in the fall and houses cool down. It doesn't require a profound temperature drop. We're talking about 1 or 2 degrees being enough to take a tired battery from being at just about threshold "beep" voltage to just below it. If you've got an LCD thermometer with a hi lo memory ($4 at the dollar store) and you mount it next to your smoke alarm you'll see that when it beeps, the thermometer is registering the coldest temperature of the last few weeks. You'll also be well on your way to geekhood. (-:
We're coming up on the ideal test period. This is the month that a lot of so-so batteries will lose enough power from the cool down to cause a low-voltage alarm, especially on a night when the temperature drops 30 or 40 degrees.
Let's see what people report. Did I say I am also fire, smoke, CO2, Radon and flood detection obsessed? It's the temperature drop. Really.
We certainly have enough theorists in this group to put this issue to rest. (-:
-- Bobby G.
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Joe J wrote:

Dunno. The rule of thumb is to replace them twice a year (when the Daylight Savings Time switches). Inasmuch as modern smoke detectors usually fuss at you when they begin to deteriorate, I suspect the replacement interval can be extended past the standard six months.
Someday there will be a mains-powered smoke detector with a battery that gets charged during normal operation, much like the button battery in a computer.
Save the batteries you remove in a specially-marked container. Use these used batteries in non-critical applications (radio, toys*, etc.). Batteries in smoke detectors draw a miniscule amount of current and smoke detector batteries typically approach their shelf-life even when installed (shelf-life is measured in years).
I put a sticker on my alarm batteries with the date of installation.
------- *You can make a friend: Got a grandkid or a neighbor's child that could use them?
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I think you will find that the "button" batteries in a computer are really non-rechargeable lithium and will need replacing after a number of years.
Charlie
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On 9/23/2011 9:37 PM, Charlie wrote:

Way back in the 386 and 486 days they still used ni-cad's. Somewhere after that they changed to lithium.
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that
really
years.
That's what I recall. But that said, my Fujitsu tablets use an incredible rare and oddball string of rechargeable button cells to power their CMOS. They use 400MHz Pentium and 500MHz Celery processors. Don't know why they went with rechargeables. I think they expected them to run out of their cradles for long periods of time. Not looking forward to replacing them as there's not a cubic mm of space wasted anywhere. Worse than that, things are packed so tight that the damn units are full of mylar insulating squares where apparently things got too close.
-- Bobby G.
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Most PC's I've seen use a non-rechargeable lithium coin cell, usually a CR2032. I haven't seen a rechargeable unit on a motherboard since my old AMI 486-50. Laptops are a crapshoot. Some use rechargeables, some don't. Not sure why.
I suspect part of the reason that alarms don't use rechargeables is that the voltage drop at the end for NiCads/NiMH is far quicker than alkaline or lithium cells. They might not "low power beep" long enough to meet safety standards as in if you've away for the weekend, the low beep could have come and gone in that time. I have seen rechargeable lithium cells in some applications, but they do have a tendency to explode if overcharged. I could see how a smoke/fire detector wouldn't want a recall risk for explosive detectors.

Batteries
That's good advice. If you rotate them twice yearly, they'll have more than enough power for a meter, radio, etc. Even once yearly on detectors that don't use much current leaves you with a battery close to nine volts. We have about 10 detectors and when our pup was young and chewed wires I snapped about 90V worth batteries of them together connected to a short length of zip cord hanging down next to her crate with a very low rated glass fuse attached to one lead. One chew through and a loud yelp and she never came near another wire.
There's 90VDC but very little current. More than enough to cure the dog's wire chewing habit. It may sound cruel to some, but the choice was to have her eventually chew through a 110VAC wire that could deliver 20A. By the time I had to build the trainer, she had already developed a taste for CAT5 network cabling which was good for a half day lost trying to figure out the failure messages.

Good idea, too. I've taken to using lithium batteries on the devices that are really hard to reach as well as the outdoor temperature/humidity transponder. I keep checking them for replacement but it's been two years and they still read 1.7 volts for the AA cells and well over 9 volts for the rectangular batteries.. That's much better performance than alkalines but at a pretty high premium. Still, if it means not climbing a ladder as often, I'm all for it. (Except, of course, that I ended up climbing up anyway to measure them so I can get a handle on how long they'll last when it *really* gets hard to go up and down a ladder.)
-- Bobby G.
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Robert Green wrote:

Next time you're up there, dangle a couple of wires down to ground level...
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If you are using standard alkaline, once a year unless you like getting woken up at 3AM on a random day. Once every 10 years if you buy 9v lithium.
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wrote:

know
woken up

That means I probably shouldn't be checking on the lithium battery's voltage every year. (-: I just started using them and I've been measuring the voltage drop (very, very little) each year to try to estimate how long they'll last. If I get ten years out of one, then it's actually cheaper to use than alkalines in the long run, and a hell of a lot more convenient, providing I can get over my paranoia about them failing suddenly. (-:
-- Bobby G.
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Joe J wrote:

Hi, My Liythium back up battery lasted 7 years. I supposes to beep when battery is low.
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Joe J wrote:

No, they don't. They recommend:
a) every 1-2 years if the unit uses a cheapo carbon-zinc or carbon- chloride battery. I used to think those types of batteries were never acceptable for smoke detectors, but one major brand came with them -- silver Eveready or Energizer.
b) every 3 years if it has an alkaline battery. This is the most common type of battery used, and they easily last 3 years, but be sure its expiration date is at least 3 years into the future. What were the expiration dates of the batteries originally in your detectors?
c) every 10 years if it's a lithium battery. That doesn't necessarily mean you can put lithium batteries in all your smoke detectors because the low battery warning is calibrated for a different voltage than for detectors designed for alkaline batteries. This was stated in the manual for our American Sensors brand (formerly Dicon) detectors, some which were for alkalines, others for lithiums.

Still the same change interval and change rules because batteries spoil even when just sitting, especially carbon-zinc and carbon- chloride.
Batteries are cheap, and it doesn't hurt to change them annually. Some people do it when daylight savings time comes or goes because they have to reset the clocks anyway, which can involve changing batteries. Be sure to write the installation date on the outside of the detectors. Silly people will object to that and claim it ruins the home decor.
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news:fe5af987-0043-

Write it with a UV pen and check it with a black light. Decor unaffected. I just picked up a CFL black light bulb at TruValue. That's a good idea, M,L&C. I've got the pen and an alleged UV flashlight populated with UV LED's that's not nearly as effective as the fluorescent bulb type.
-- Bobby G.
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