Hello, you can make settings on the unit to determine the humidity level at which the unit becomes "active". It switches on automatically as soon as the humidity falls below the setting. You can leave it connected to the power supply at all times. It goes into standby mode when the water tank is full.
This does work. However, the operating instructions (which can be found with Google) forbid it in the "Safety" section. In addition to Bruno, I can also point out the built-in timer function.