I've have an old PEQ motion sensor mounted outside on a lamp post, exposed to New England weather for 4 years. I got it used, where I think it think the original owner had used it outdoors for over 4 years, too (@mike.maxwell?). Tracing it's origins, it have been in this: PEQ at Best Buy - #126 by Mike_Maxwell - Connected Things - SmartThings Community.
For me, it had lasted 3 years on the first CR123A battery, but only 12 months on the latest battery (I record this in a spreadsheet).
It got flagged as not being active for 24 hrs by Device Activity Check, and given that the battery was only in there for a year, I wondered why it had died so soon. So I went to replace the battery, and when I opened it about 50 tiny ants were inside the lid. I shook out the base and another hundred ants came out. I put it down and took this picture:
Those tiny black specs are some of the ants. This picture is before I opened the case - there were still few hundred more of them inside at this point.
After that I took it all apart, used compressed air to clean it out the gunk, and then put it back together with a new battery. I had to reset it and the re-pair it.
Still working fine. 
I did spray around the lamp post with RAID before putting the sensor back on top.
