When you change your clocks in the spring and fall you should also replace the batteries in all of your smoke detectors. Also it's a good idea to vacuum your detector, so that cobwebs and dust particles do not prevent the detector from working properly. If your smoke detectors are older than 10 years old, you need to replace them.
Detectors only work properly for about ten years.
Smoke detectors can be purchased from most hardware and general drug stores. Smoke alarms are required outside each separate sleeping area and on each level of your house, including basements, but excluding unfinished attics and crawl spaces. If you have a high - pitched ceiling, mount the alarm near the highest point. In general, you should put your alarm squarely in the path smoke would probably take if it were heading upstairs or through your home, toward your bedrooms. That's when most fire deaths occur.