Wired smoke detectors are often the last line of defence between a homeowner and a house fire. Designed to sound an ear-piercing alarm the moment smoke comes within a certain distance of its sensor, a smoke detector can often save lives by alerting people to a fire they may not have realised was there until it was too late. Although a wired smoke detector will operate off of your home's electricity, it also uses batteries for backup power. If you ever lose electricity to your home for whatever reason, your smoke detector will still be able to function off the power generated by these backup batteries. They must be changed often to ensure the detector will always be there when you need it.
Take off the smoke detector's cover. Depending on the model, you may have to remove some screws in order to get the cover off. Regardless, most models require you to twist the cover and "unscrew" it, which will reveal the wires and batteries inside.
Remove the old batteries. Depending on the model of wired smoke detector, it could have a single 9-volt battery or a few AAA or AA sized batteries. Take the old ones out and throw them away. If you keep them around it could be easy for you to confuse them with fully functional batteries.
Put replacement batteries into the wired smoke detector. If it is a 9-volt battery, it will go into place only one specific way. If they are AA- or AAA-sized batteries, be mindful of the directions. The positive side of the battery must go into the detector a certain way for the unit to operate. The directions will be printed on the smoke detector itself.
Replace the wired smoke detector's cover. Screw the cover back on by twisting it in the opposite direction you did when you took it off. If you removed any screws, screw them back in at this time.
Change your batteries every six months whether you need to or not; a good rule of thumb is to replace the batteries in your smoke detector every time you have to change your clocks for daylight-saving time.