Generally, batteries should be changed-out on a regular basis. I'm not sure if it was the Battery Companies that suggested this but these days, you'll hear the 'general rule' is to change them every time you change the clocks (which is every 6 months.) This would ensure a strong, fresh battery all the time.
Now, you COULD 'play' with this rule and let the alarm tell you what's up. This is your case. Most likely, the battery is running low or the 'sensor' is dusty. Dust can cause the alarm to get a false reading. If you have a battery tester at home, you'd set the switch on it to DC, then set it to 'read' 9v (assuming your alarm uses a 9v battery), and go from there. If it's less than 9, then it's starting to 'drain'. Change it!
As the battery gets drained, the chirping will get more frequent. Unless you are a masochist (just having some fun) where you 'like' getting woken up in the middle of the night by this chirping, leave it alone until you can't sleep. BUT, if you're like most folks, I'm sure you'd just assume that it's time to change the battery. :-) It's your life and your home you're trying to protect.