Seeed 101020037 Grove Touch Sensor Capacitive Sensor based on TTP223-B

The Grove Touch Sensor module is an ideal alternative for a mechanical pushbutton. The simple device uses the TTP223-B touch detector IC to measures the capacitance of a metallic pad. When a finger is near or on the pad that sensor detects it an actuates the switch. As the sensor detects the proximity of the finger as well as direct touch, there are many ways to use this module. You can place the metallic pad under a non-metallic surface such as a plastic sheet, glass/wood table, etc. Great for projects that need to be waterproof. Why not construct a hidden button to stylishly actuate a device.