I sold & installed alarm & access control systems for 10 years and learned that you can “pet proof” your passive infra-red (PIR) detector from being triggered by masking the lower sections of the sensor so that it ignores movement in the lower areas.
To do this, take the sensor apart and behind the translucent cover you should find either the inside of the cover or another semicircle of plastic inside that has smallish (1/4"-1/2") square sections that are light guides into the tiny sensor in the back. These sections are the “zones” that direct light from the room into the sensor and the more sections there are, the more flexibility you have for detection. These zones are in a grid and in order to pet-proof specific areas of the room, temporarily mask them one section at a time with small post-it notes in the lower sections where your pet can trigger it.
Test your work and watch for the unit to be triggered (or not). Be careful of pointing the detector on radiators, heat vents and windows too. When you are satisfied with the masking/pointing, then replace the post-it masks with duct tape. You can always add more later if you missed a spot. If you are working with Microwave-type sensors, you will need to use heavy aluminum foil.
IMHO, alarm monitoring is a waste because their is no accountability for performance, accuracy or timeliness. I would never be confident that my place is protected by such a simple system, simply because an intruder can find and disable this system in less than a minute - if triggered. With only one PIR sensor, you cannot enjoy “double coverage” where two detectors “watch” each other. This means that only one area is going to be covered and this is a compromise. An intruder can see the detector before it sees him and can avoid detection by skirting the protected area - and that means he can search for goodies and the control unit at his leisure. Out of good taste I will not recommend competing/better products though.