We have recently moved in to a house fitted with a Scantronic 9448 alarm system. We believe we need to replace the PIR detectors to pet tolerant ones (as we have two house cats) and I wanted to check before I go ahead and purchase them that the 430 PIR will be compatible with the existing system?

Yes the 430 pet tollerant detector is compatible with the Scantronic 9448, but be aware that pet tollerant sensors false alarm with cats because they climb. Most pet tollerant sensors dissregard the area about two to three feet from the floor. When the cat climbs onto the table or back of chairs or work surfaces, this will produce a false alarm in many occasions. Also these sensors can not be pointed towards the stairs.