A while ago I discovered four extra bits in the UPM temperature RF protocol. Two of the bits are sequence counters which simply adds one for each message in the three message bursts sent by the sensors. The other two bits seemed to be some kind of checksum. I have had some reports of people getting bad readings sometimes, so I finally took the time to figure the checksum out. After a bit of experimenting and analyzing, I finally managed to decode it: Bit 0 is all even bits in the message XOR:ed together and bit 1 is all the odd bits. So now bad messages will not be reported from the receiver any more!