XPA-CB-14017-APO XPander Heat Detector (A1R) with Sounder BaseXPA CB 14017 APO XPander Heat Detector (A1R) with Sounder Base The XPander Heat Detecto utilises an open web casing which allows air to flow freely across a thermistor which measures the air temperature every 2 seconds. Its microprocessor uses algorithms to determine how fast the temperature is increasing and thus be detected at an earlier stage than with a static detector. A rate of rise detector is generally preferred to a static heat detector,