I’ve got two of the FGMS-001 sensors – one outside my front door and the other outside the rear patio door. I’ve had them out there for just about 3 years now.
The one in back is well protected from rain under the patio covering. The one in front is under the eaves, and is only partially protected from rain. I have had no problems with either. I’m in Arizona, so they see occasional very heavy rainfall, and a temperature range of about 20°F to 115°F, and bright sunlight with a UV index of up to 12 according to my weather station.
I don’t use them to control lights but just for security, and in the case of the one outside my front door, to trigger an audio announcement that lets me know when packages are delivered (since those folks don’t ring doorbells anymore).
The FGMS-001’s are really sensitive, and I ultimately found that setting the sensitivity on 85 kept it from triggering on the desert critters. The one in front of my house still triggers (maybe once a month or less) when a bird flies within a few feet directly in front of it, but I can’t adjust the sensitivity any more or else it won’t reliably detect people.
If you’re OK with bird false alarms, I don’t see any reason why you couldn’t use it to trigger a light. To my knowledge, the one in front has never failed to trip on a person (based on the appearance of packages!).
I also have two Zooz ZSE-09 sensors outside (look exactly the same as the FGMS-001) that I use for detecting when the sun is shining (vs. cloudy) as part of my window shade control logic. One is totally unprotected from the rain. I tried the ZSE-09 because they are cheaper than the FGMS-001, but I was never happy with the ZSE-09 motion detection, so that’s how they got relegated to sun sensor duty.
I’m surprised how waterproof that little ping pong ball shell is on the Zooz & Fibaro devices.