Invensys MN-S-3 MicroNet Sensor. Have 22 of these in good condition, and 4-5 more good for parts (a few are Siebe brand, but the same device). No warranty, but they were functioning when we took them out of our building. $125 on ebay, so only $95 each here or all of them plus the spares for $1800. Getting hard to find, so if you need some, here you go. Pickup at my office unless we arrange something else. No scammers, please.