A regularly-chirping fire alarm isn't just annoying. It's also a sign that something is amiss. There are several possible causes, including:
A loose battery. Try taking the battery out and re-securing it.
A dirty fire alarm cover. Vacuum the sensor chamber twice a year to prevent build-ups.
You may need to reset your electronic fire alarm after installing a new battery
A power surge interrupted the fire alarm. Resetting the alarm will stop the chirping.