Consider an example in which the sensor is a PIR detector, for example, which senses the presence of one or more individuals. Consider the situation in which operations are started and the sensor is not activated because no one is present. In this case the microprocessor no initialises “?1 State” and “?2 State” to zero (block 210) and enters the first deep sleep configuration (215, 220). Hence the microprocessor will wake up in response to either a signal from the sensor or expiry of the timer. Operations are then paused in block 230 until the microprocessor no is woken up. Since no one is present the microprocessor no will not wake up until the timer (of duration=“Sensing Time”) has expired. The procedure then reaches block 320. Since “?1 State” is zero, the operations of block 335 are executed. “?2 State” and “?1 State” are not changed by these operations and thus both remain with the value zero. A confirmed absence is then sent to the server (block 340). The microprocessor no enters the second deep sleep configuration (345, 350) and so will only wake up within the current operational period if it receives a signal from a sensor. Operations then pause at block 230 until a signal is received from the sensor. Therefore, no unnecessary further “absence” signals are sent to the remote server 16o, thereby reducing signal traffic and power requirements. The microprocessor no is now in a state in which it is “primed” to react to a signal from the sensor.

Suppose now that an individual enters the occupancy space and is detected by the PIR detector. The microprocessor no is woken up in response to receiving a signal from the PIR detector. Hence, the procedure continues via blocks 240 and 250 to block 270.