No, motion detector technology has come a long way and most manufacturers now offer a “pet immune” version of their sensor. These “pet immune” sensors have reduced sensitivity so that an animal under a certain size will not activate an alarm. Sensors are usually sold with “pet immunity” weights such as 40 or 80 lbs. Additionally, you can always mask off the bottom of your motion detector lens so that it will not pick up motion at the ground level. This allows your animal free range while still protecting you against real intruders.