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We have 2 Norelco smoke detector in the house. Early this morning, one of them began issuing short "battery is low" beeps every 5 minutes. The batteries for these detectors are 9v. I replaced the battery in the one that was beeping with a Gettop (Chinese) battery that I've never used for anything before. After doing so, the detector started issuing beeps about every minute. Thinking they battery must be run down or defective, I measured the voltage. To my surprise, it was 10v, not 9. I then checked to see if the contacts in the detector had become corroded. They hadn't. I then replaced the Gettop with a Duracell 9v, and the detector no longer beeped/worked perfectly.

Thinking perhaps that detector might have become faulty, I tried the Gettop in the other detector downstairs. Same result; immediately started issuing short beeps at 1 minute intervals.

Why is the Gettop unusable in these smoke detectors? Is it because they're intolerant of batteries putting out 10v (even though it says it's a 9v on the label)? Has anyone else had a similar problem with Gettop batteries?

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closed as off-topic by Dmitry Grigoryev, Maple, RoyC, Sparky256, Brian Carlton Sep 11 '18 at 2:16

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – Dmitry Grigoryev, Maple, RoyC, Sparky256, Brian Carlton
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    \$\begingroup\$ Is it because they're intolerant of batteries putting out 10v .... how do you know that the voltage was 10V when inserted into the detector? \$\endgroup\$ – jsotola Sep 10 '18 at 1:05
  • \$\begingroup\$ The smoke detector can not read the batteries label, just the Voltage. It is not that hard to believe that a circuit will not function correctly with over voltage \$\endgroup\$ – PlasmaHH Sep 10 '18 at 7:11
  • \$\begingroup\$ I know the voltage was 10v because I measured it both out of and connected to the detector. Same reading whether or not it's connected. \$\endgroup\$ – Don Taber Sep 10 '18 at 20:19
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    \$\begingroup\$ Smoke detectors have a limited life span. They use the radioactive element americium (or an alternate) which decays as the years go by. This is how the sensors detect smoke and some gasses. In less than 10 years or so its radioactivity is so weak it is no longer of any use, in which case the alarm will always sound even with a good battery. \$\endgroup\$ – Sparky256 Sep 11 '18 at 0:37
  • \$\begingroup\$ These detectors are at least 30 years old. I'm aware that they use a radioactive element, but the half-life of most radioactive materials is extremely long, so I figured they would last at least my lifetime. To test that, I just went to the one at the top of the basement stairs and lit a match under it. Within 10 sec., the detector went off with a piercing continuous beep that continued at least 3/4 of a minute while I diffused the fumes with a towel to get it to stop. So the hypothesis that detectors are only good for 10 years may be true for some, but is not true for the one's we have. \$\endgroup\$ – Don Taber Sep 12 '18 at 13:17
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I would expect a fresh 9V battery to put out slightly more than 9V. A 9V battery is made using a stack of six 1.5V cells, and each of those can easily put out 1.6V when new.

I suspect the reason the smoke detector didn't like the battery was that its internal resistance was too high, causing the voltage to drop whenever it did a self-test. Smoke detector manufacturers usually specify certain brands of alkaline battery - though I find that any decent quality one normally works fine.

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