OK so AC rocker switches aren’t very sexy, these from OMRON don’t even look any different from standard switches. But they have a very useful feature. There are two basic models in the range. The standard A8GS has a built-in actuator which allows the rocker switch to be flipped off by applying a 3.3 or 5 V control pulse. It is the smallest switch yet to offer this reset feature.
The A8GS-T also has an ‘off’ actuator and a secondary ‘signal’ contact. When the switch is flipped on, AC is supplied to the equipment and the signal contact closes. At turn off the switch action only opens the signal contact; AC to the equipment is maintained. This would typically be useful in a microcontroller system which reads the signal status and performs essential housekeeping tasks (e.g. storing data to non-volatile memory) before it issues the 'off' signal to the switch actuator. The switch does not need to be manually turned off; the equipment can issue the off signal as and when necessary.
Although this feature gives an orderly shut down sequence in normal operation it will not give the same protection during a power outage.