It saves children from electric shock when they touch sockets with wet hands. The humidity sensor installed cuts the electricity with relay when humidity level exceeds certain critical value - it means it also breaks circuit when there is a potential hazard, when the environment around it is wet.
The user can also manually break the circuit remotely via smartphone. When you’ve just remembered that you’ve left an electric heater or spinning fan on and there is a toddler wandering home you’d definitely want to turn it off right away.
Humidity sensor is connected to coil and coil inside the socket detects water. Its mechanism is very simple. (See the schematics.)