A method for adaptively adjusting a threshold used to detect the presence of a living being may include receiving a first set of sensor measurements acquired by a passive infrared (PIR) sensor during a time period when the living being is not expected to be present in a space monitored by the PIR sensor. Here, the sensor measurements may depend on one or more noise sensitivity characteristics of the PIR sensor. The method may include adjusting a threshold that may indicate a presence of the living being based on the first set of sensor measurements. The method may then receive a second set of sensor measurements acquired by the PIR sensor and detect the presence of the living being when at least one of the second set of sensor measurements exceeds the threshold.