high the combination of sensor reading level and rate of rise then can be show as a table as show in table 1 table 1 provides examples and is provided by way of explanation not limitation one of ordinary skill in the art will recognize that the notice level n can be expressed as an equation n f t v r where t is the threshold level v is the sensor reading and r is the rate of rise of the sensor reading in one embodiment the sensor reading v and or the rate of rise r are lowpass filtered in order to reduce the effects of noise in the sensor readings in one embodiment the threshold is computed by lowpass filtering the sensor readings v using a filter with a relatively low cutoff frequency a filter with a relatively low cutoff frequency produces a relatively long term averaging effect in one embodiment separate thresholds are computed for the sensor reading and for the rate of rise in one embodiment a calibration procedure period is provided when the sensor unit 102 is powered up during the calibration period the sensor data values from the sensor 201 are used to compute the threshold value but the sensor does not compute notices warnings alarms etc until the calibration period is complete in one embodiment the sensor unit 102 uses a fixed e g pre programmed threshold value to compute notices warnings and alarms during the calibration period and then uses the adjustable threshold value once the calibration period has ended in one embodiment the sensor unit 102 determines that a.