Since the average kind of pet can be detected by the PIRs as intruders, there is a risk of false alarms. However, by using pet friendly PIRs which can distinguish pets either by the body mass or body heat radiated, or by the mass volume of the shape of the animal, the risk is minimized. Additionally, pet friendly PIRs can be set not to activate the alarm if there is moving heat up to a certain height, such as 40cm, which is the normal height of an average dog, hence, decreasing the risk of a false alarm. To further decrease the risk, door and window contacts can be used instead of PIRs. These work on the principle that the alarm is triggered only when a door or a window is opened, which is something that a pet (typically) cannot do.