Smoke detectors can use different types of batteries, but the most common ones are 9V and AA batteries. The 9V battery has been the battery of choice for smoke alarms for many years, but nowadays, it is more common to see two or three AA batteries in smoke detectors. AA batteries have about three times as much energy as a 9V battery. Smoke detectors with replaceable batteries are more affordable and budget-friendly compared to those with built-in batteries.

It is important to check the batteries in your smoke detector consistently and replace them every six months. A good reminder is to change your smoke detector batteries every time you change your clock for Daylight Saving Time. Some smoke detectors have a built-in battery that lasts for the life of the detector, eliminating the need for battery replacements. These detectors are powered by sealed lithium batteries with a life span of 10 years. When the batteries are weak or the detector malfunctions, the whole device will have to be replaced.

In summary, the size of batteries that smoke detectors take can vary, but the most common ones are 9V and AA batteries. It is important to check and replace the batteries every six months to ensure that the smoke detector functions properly. Smoke detectors with built-in batteries are also available, but they are more expensive and need to be replaced entirely when the battery dies.