There are numerous threads on here about petwise, pet tolerant, pet immune sensors.
The smaller the animal the less of a risk of a false alarm, limit there access to the house when out and perimeter protection are better options.
I have been to numerous properties where the customer is relatively short and cant activate a petwise sensor, even been to houses were a step is the difference between them being detected or not (6 inches ish).
With wireless sensors you have to be wary of them sleeping, so been to many houses where they think the installer has pulled a fast one , only to show them that if they have just walked all round the house the pir's are sleeping, get them to put the kettle on have a few sips then do the walk test and show them all working. (sleep is about 3 mins) kettle boil time is about 2.5 to 3 mins...but if they have fast boil kettles or instant boil out of the tap it screws my timing up!
Mmm ok. Thanks for reply. OK. so maybe fit proper (non pet modified) sensors upstairs / downstairs along with glass and window sensors downstairs and deactivate the PIRs downstairs when the pet is at home!