Test smoke alarms monthly and replace them every 10 years
Added
NFPA says to test alarms monthly and treat chirping as a signal. A single chirp every 30 or 60 seconds means a low battery. Chirping after you've replaced the battery means the alarm is at the end of its life. Look for the manufacture date on the back of each alarm.
The result
Result: NFPA: all smoke alarms must be replaced 10 years after their manufacture date.
Source
NFPA (opens the original source in a new tab). Check it for the latest numbers before you act.