Why you always want enough spare batteries for all you smoke and CO detectors.

Smoke detectors using 9V batteries have a warning beep, when the battery gets low. This will keep beeping until the battery dies or has been replaced. A few handy facts to know:

- The batteries have a lower voltage when it’s cold. Since the temperature drops during the night, the beeps usually starts during the night. This is also why sometimes it seems to disappear in the morning and come back next night.
- If you have multiple detectors, the threshold for the beep to start varies between detectors. So using a multi meter of battery checker might not find the one which is beeping.
- NiMH and Lithium batteries have different voltage properties so depending on the detector it might start beeping to late or too soon.

If you do not want to wake up at night from the beeps, make sure you replace the batteries on time. If it still beeps, make sure you have enough batteries to replace them all. Finding the correct detector can be hard and is rather annoying in the middle of the night. Replacing them all at once and get back to sleep. Trust me, I have 5 detectors (smoke, heat and CO) and all in a small apartment.

Other things to note:
- Make sure to cap or tape of 9V batteries after use to prevent short circuiting
- The detectors have expiration dates too. When you use them to long, the detectors become less sensitive.