My experience with this type of sensor is that they do just that i.e. sense pets. Having said that, knowing where and how to set them up properly according to the manufactures instructions gives reasonable protection with a small risk of unwanted (rather than false) alarms.
The same goes for perimeter detection, if you set them up according to manufactures recommendations and instructions you are usually relatively free from unwanted alarms.
Because of the nature of pets I don't think any manufacturer will guarantee that pets will never activate the alarm devices even if they are for so called "pet avoidance"
I always recommend that pets are kept out of any alarmed areas if this is possible (and it always is one way or another) if not then the risk of occasional unwanted alarm must be accepted as part of the situation. In turn too many unwanted alarms will affect the response from the authorities and also the insurance in many instances and that is apart from key holders who may be fed up to turn out and of course neighbours who get fed up of the sounders going off