If it's a 120V with battery backup, the battery may be going dead. Or it may need cleaning - use a vacuum.

If cleaning it, or replacing the battery doesn't solve the problem you should replace it. The National Fire Protection Association recomends that any smoke detector more than 10 years old should be replaced.

Jim Simmons
WA State Master Electrician

and if an integrated system (where detection in one area of home triggers ALL to alarm) could also be an indication of a failure of wiring or in another area as well. When replacing be sure if integrated that you replace with the proper one (rated/designed for the location, i.e. kitchen, bedroom, hallway, etc.).

The useful life of detectors is average 7-10 years as they coating on the "detection strip" is actually a radioactive substance that decays over time. Additionally they can become coated (smoke, soot, grease, etc.) and also not operate properly.

Smoke detectors are supposed to be checked monthly (using test button), have back-up batteries replaced at least annually (most now recommend every six months and the "changing of the clocks" as a home-maintenance reminder), and be "smoke stick" tested for reaction at least every three-six months.

Also keep in mind that previous legitimate exposures causing the detector to "alarm" will expidentially reduce the useful life of the detector (strip becomes coated, inlets and airways clogged).

Furthermore detectors are supposed to be kept clean and be vacuumed every month (dust, cob-webs, insects, etc.).

Ell.