There was an earlier thread on this subject that is now closed, but it doesn't hurt to bring up the subject again.

When doing your PDI, make sure the smoke, CO and LP detectors (as appropriate) have good batteries installed, with correct polarity and that any paper or plastic tabs put between a battery and the contacts from the detector manufacturer are removed. Push and hold the button on each unit to test it.

This is one of those things I didn't think about, assuming that stuff would get taken care of at PDI. It entered my mind a few times since we purchased our trailer six months ago, but I either didn't think to check or it was inconvenient to (going to bed, heading out the door, away from the trailer, etc.). I finally remembered to check during a convenient time the other day and found that the detector in the bedroom wasn't working (had an old/discharged battery in it) and that the smoke detector inside the front door of the coach still had the plastic tab in place between the battery and contacts. Both are now working.

And yes, any time is convenient to check your safety equipment.