After a safety function has been requested the safety relay module only switches on again once a reset button (also referred to as start button) has been actuated.

The contrary is the operating mode "Auto start" (Automatic start), which is only admissible under certain conditions (if there is no danger of an unexpected restart) or a reset comes from somewhere else (with a quality corresponding to control category 1 to EN 954-1). Not admissible, for example, in emergency-stop command devices, in accessible rooms etc.

"Trailing edge" or "Edge detection" in this connection means that it is not the rising edge (upon actuating the button) that generates the start signal but the trailing edge after releasing the button. The analysis of the trailing edge or edge detection is an additional safety measure before an unexpected restart in the case of a manipulated or defective button.