Combined smoke and heat detector with replaceable smoke chamber, Optical smoke and heat detector, four-wire, supply voltage 8.5-33 VDC, With changeover relay output, self-resetting IP43. All Aritech 700 series smoke detectors continuously monitor their sensitivity and operating status. Background drift is compensated daily to maintain the original calibrated sensitivity within the required limits. Once a day, the detector performs a full diagnostic test that includes dynamic testing of the sensing chamber and internal electronics. If a detector goes outside the sensitivity range or fails the internal diagnostic test, this is reported back to the panel and indicated on the detector as a fault with a yellow diode.