A compound sensor system includes a first sensor, a second sensor, a memory that stores a module, and a processor coupled to the first sensor, the second sensor, and the memory. The first sensor is configured to detect a parameter that indicates a likelihood of having a user enter or leave a target area, and, in response, send a first command signal to the processor. The processor is configured to receive the first command signal from the first sensor and send a second command signal to the second sensor based on receiving the first command signal. The second sensor is configured to operate at a sleep mode and switch to an active mode upon receiving the second command signal, and during the active mode the second sensor is configured to determine if the user enters or leaves the target area.
