1) Both Smoke and Carbon Monoxide Detectors have an expiration date. Usually 10 years beyond the Manufactured date.
2) Detectors will chirp or beep every specific time period (usually) 60 secs to alert you that the detector is outdated or the batteries are low. Replace the batteries, if it continues replace the unit.
3) NO MATTER the reason if you feel uncomfortable that your alarm is going off or making any kind of noise call 911 and have the local Fire Department come check out.