SL-166A：With door position detection output (N.C. ) SL-166B：With door position detection output (N.O./ N.C.) SL-166U：With DC 12V~24V power supply Note： SL-166 has its own micro-computer control and detection. It is strongly suggested to use its own door open point (N.O. point) to open door and do not turn its power off (N.C. point) to open door.