In a recent thread:
http://www.fiberglassrv.com/forums/f...tml#post369172
The S word came up. It reminded me of when I was calibrating the Lower Explosive Limit (LEL) gas detectors on a 500 hp gas compressor. When, the unit abruptly ceased to function. I went inside, the building guys were doing some silicone work on the
windows. It turns out, the vapor given off kills catalytic bead sensors, dead.
These are likely the same technology as your
propane detectors, or natural gas detectors. If you have siliconed any where near them, especially if the
propane detector was operational, it might be dead. BTW, they also just wear out. Replace at least as often as your smoke detectors.