Smoke alarms have an expiration date. I have always tested our smoke alarms monthly and assumed that as long as the alarms beeped when I tested them, they were fine. I learned recently there’s an expiration date printed on the back of the smoke alarm, and that when you test the alarm and it goes off, that simply means there is power to the alarm. But if the alarm is older than the date printed on the back, there is no guarantee that it will sound when it needs to.
So check your smoke alarms and put a note on your calendar so you’ll be sure to replace them at the right time.
P.S. I checked my carbon monoxide detector, too, but it doesn’t have an expiration date. I’ll be looking into that in the future.