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?
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.
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.
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
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.
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
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
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.
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
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
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.)
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. (-:
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
Still the same change interval and change rules because batteries
spoil even when just sitting, especially carbon-zinc and carbon-
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.
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.
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