The motion sensor V2 works fine for a few days or a few hours before triggering a false alarm. This has now happened several times. The unit had previously functioned fine for a couple of years. Fresh batteries and deleting reinstalling did not solve the problem.
Could the sensor’s electronics have aged such that it is no longer reliable? Or, is there chance that it picks up motion from an insect crawling across its face? Any suggestions will be appreciated.
That is absolutely possible.
However, since the motion sensor determines motion based on heat, this time of year, a lot of false detections are due to HVAC changing the ambient temperature in waves. So it is possible that it is picking up the vent pushing heat out, or something similar. Sometimes a slight repositioning can help resolve this sort of things.
But since you didn’t have this problem for a couple of years and now you suddenly do, it seems the HVAC thing is not likely or you would’ve seen it in the past.
Other things I’ve seen cause false PIR detections include: nearby electronics causing electrical interference. Humidity apparently sometimes oddly affects them. Drafts.
You don’t have pets?
As you said it is possible that things are just aging in it. If you have more than 1, you could try swapping places with another one and see if the issue continues after the swap. That would be really telling. If you don’t have more than one, you could still potentially take it down and put it somewhere that it can’t sense any heat/motion and see it if it still triggers. You could put a camera somewhat near it and see if the camera detects what might be triggering it when the false detection happens…just make sure the camera isn’t going to cause the detection.
Excellent suggestions. Thanks very much! I’ll just swap with another sensor to determine whether the issue is related to the unit or the position.
Excellent! You have more than 1. I was hoping for this. Another thing you could do is put both of them somewhat next to each other and if one triggers and the other doesn’t, that would be pretty telling that one of them is likely glitching. But if they both “false trigger” at the same time or close to each other, then it must be environmental.
You have a few good options to test it out since you have 2. 
Feel free to check back with your findings as it could be useful to others in the future too.