BLTouch is an auto leveling sensor for 3D Printers that can precisely measure the tilt of Bed surface. It could work with any kinds of bed materials, such as glasses, woods, metals, and so on. BLTouch is fulfilled with simple structure and high precision by using progressively designed solenoid and hall sensor. It aims for user convenience and enjoyable printing by adding many smart functions, such as self-test, alarm, alarm release & Touch Switch mode, Blue LED for servo signal indicating and Z-probe(Zmin) Testing. Self-test : The push pin operate two times in a test when the power is on. Alarm : The LED light blinks if a problem was found on a self-test or during operation. Wiring defect indicator : Blue and Red LED for indicating wiring defects.