The System Sensor M02-04-00 Replacement Test Magnet is a specialized diagnostic tool designed for testing smoke detectors and duct smoke detectors used in HVAC systems. It works by activating the detector’s internal test function, electronically simulating a smoke condition without the need for actual smoke, allowing technicians to verify sensor performance, alarm response, and contro... https://www.partshnc.com/m02-04-00-system-sensor-replacement-test-magnet