Kidde has replaced its model 1275 ionization smoke detector with model i12040, but whether you have the newer model or the older now obsolete model, you follow the same procedure to replace the battery. Both units use a 9-volt battery, which can be a carbon-zinc, alkaline, or lithium type. Kidde does specify battery recommendations in the user's manual for the i12040, but its recommendations cover most of the leading brands available at stores, so basically, any 9V battery that you didn't purchase at a dollar store will work.
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Keep in mind that if you have a model 1275, it's probably time to replace it. Smoke detectors are designed to last for 10 years, and if you keep using one past this time, your protection from fires is greatly reduced. When you go to replace the battery on your model 1275, check the manufacture date, and if more than 10 years have elapsed, consider replacing it with a model i12040.
How To Replace the Battery
The battery compartment is located on the back of the unit, and to access it, you have to remove the smoke detector from its mounting bracket and disconnect it. To do this, twist the alarm 1/4 turn in the direction of the "off" arrow imprinted on the mounting plate, and when the tabs on the alarm line up with the notches in the mounting plate, you'll be able to pull down the alarm. Disconnect the alarm from power by pulling the quick-connect plug apart.
Turn over the smoke detector to access the battery compartment, lift the tab on the cover, and remove the cover. Pull out the old battery and read the battery installation instructions on the battery cover. They will tell you to depress the battery reminder finger inside the compartment as you install the new battery. If the battery isn't holding down this finger, the battery door won't close. With the new battery properly installed, reconnect the smoke detector to power and twist it into the mounting plate in the opposite direction to seat it.
How To Stop the Chirping
Kidde 1275 and i12040 smoke detectors are equipped with a warning feature to alert you to improper battery installation or low battery. The chirping is designed to occur at irregular intervals. If it has been a while since you serviced the smoke detector, this chirping means you need to change the battery, which is typically supposed to last for only one year.
When the smoke detector chirps after you have just replaced the battery, it means the battery hasn't been properly installed. To stop the chirping, take down the alarm, disconnect it, remove the battery, and reinstall it. Hopefully, you'll get it right this time, but if not, keep trying until you do. The battery terminals are inside the compartment, and the battery has to be in complete contact with both of them. It's also possible you put the battery in the wrong way, so if you can't get the chirping to stop, remove the battery, turn it over, and reinstall it.
Smoke Detectors Need Regular Testing
At regular intervals, it's important to test your smoke detector to make sure it's working properly. You do this by pushing the "test/hush" button on the front for five seconds until the alarm sounds. If the unit is part of an interconnected network, all the alarms will sound, so be ready for a lot of jarring noise.
If nothing happens when you push the "test" button, the unit may not be getting power from the circuit, so check the circuit breaker. If the unit does have power, the green LED on the cover should be lit, and if that's the case, the battery is weak or dead. If this turns out to be true and the smoke detector hasn't been chirping, it's probably defective and needs to be replaced.