I rented a house with some smoke detectors. After a couple of years they strated beeping - all within a month of each other. I changed out the batteries - still beeping. Changed the batteries again - still beeping. Checked the wiring - still beeping. Unplugged them - still beeping.
I find it odd that ALL THREE did this around the same time. If it were one I would assume an electronic componant failure, so did they just wear out?
You are supposed to change them out after about 10 years or so, they do not last forever. I am not aware that they will start beeping when they wear out, though.
These are smoke detectors only, not smoke/carbon monoxide detectors, right? If it detects CO as well, I’d first be concerned about a CO problem, not a detector problem.
Smoke detectors (assuming you’ve got ionization-type detectors) use a small amount of Am-241. Considering that the stuff has a half-life of about 400 years, my guess would be an electrical problem with the ionization chamber. Honestly, I’d just replace them, probably with the intergrated CO detectors if you’ve got a gas furnace or water heater.
I figured better safe than sorry. I’d hate to find out that they did wear out the hard (and death-filled) way. The replacements were $15 (no not detecting CO) and I have no clue how long they were there before I moved in.
If the detectors were photoelectric, there’s a possibility that cobwebs or other crud in the sensing chamber caused the activation. Since they are interconnected, a fault in the warning circuit of one can adversely effect the others. The NFPA recommends replacement after 10 years as Cheesesteak mentioned, so you’re better off anyway. 
Yes, they wear out. You can stave off that time by vacuuming the detection chamber. However, if your life and the value of everything you own is worth more than new smoke alarms [Jack Benny] “I’m thinking!” [/Jack Benny] and you don’t know that your alarms were new when you moved in, go buy some new ones.
This is serious, SaintCad. Don’t wait. Two years ago, I read in the Indy Star about a family that got a smoke alarm for Christmas. The next night they woke up to a loud beeping from inside the box of the not-yet-installed alarm. No one was hurt, they all got out safely.
Really, this sounds like an Urban Legend to me.
Every smoke detector I’ve purchased did NOT have the battery installed, just contained separately within the box. Given the long time a smoke detector might sit in warehouses & a store before being sold, why would a manufacturer actually connect the battery when building it? Especially since that would require more labor & raise their production cost. And could result in a brand new smoke detector with a run down battery, leading to customer complaints.
Do you have an actual cite for it?
(I can’t find it on the Indianapolis Star site, but that’s not surprising if it was published over 2 years ago.)