Battery operated smoke detectors going off for no apparent reason. First, batteries were replaced and it continued to happen. Then, three new smoke detectors were purchased, installed, and all new batteries used in the new detectors. The smoke detectors are still beeping just like before -- not all the time -- but are all still doing it. What is going on? Have you seen or heard of this before? These are not wired into the security system.

Are they wired into the home's electric at all? Possibly something is not wired up correctly. This same thing happened to a new modular home that my company installed recently. It was the wiring.

Are they alarming or just beeping like when the batteries are dead. If they are alarming obviously there is some form of particulate in the air tripping them.

What else is going on when they go off - furnace fan blowing? Gas fireplace? Candles burning?

Possibly dust or dirt.
Blowing out, or vacuuming out may fix.

I have had a similar problem with one of my smoke detectors until I took it down off ceiling and noticed that the hoild in the ceiling which the wiring came through (mine are hardwired to an alarm system) was so large that it allowed dust to pass into the detector. Enough passed through that it would eventually alarm. Also if unit is in a high air draft location the air flow will act as a highway being all kinds of particles and other unseen debris into the unit. Last some units are very sensitive to very small charged particles so if you have a situation like I described above PLUS run your furnace fan all the time you will have a condition which is good to set the things off falsely.

I am aware that you placed new units in the same position and have put new batteries into them with no luck.