I have recently installed these:
Wired: Visonic K-980D Pet Immune Infrared/Microwave Motion Detector 40' X 40' Coverage, about $45.
And wireless CADNX481 Pet immunity up to 40 pounds, about $80.
I am impressed with the immunity of the Visonic set on 2 counts. The microwave is very sensitve if you desire very fast detection (set on single count) but I use it just as a check of the PIR (set 2 count) vs. the PIR checking itself like most do (w/o the microwave feature). The microwave needs actual movement so a heater kicking on, etc. would not trip a false alarm (not saying this is a problem now-a-days).
These new pet immune ones sure are less sensitive so there is a trade off there. Also the dog/pet wt. is cumulative if you have more than 1 pet (add them up). I did not know this even after I did my research! It is in the installation instructions however!