This is a simple touch sensors module. You can use it to replace a traditional push button. Using the TTP223-B touch detector IC It measures the capacitance of a metallic pad. It can detect the change in capacitance when a finger is near it. This is the same technology used in the iPhone touch screen. So you can place the metallic pad under a non-metallic surface such as a plastic or glass sheet and it will still work as a button. This may be useful for projects that need to be waterproof. You can also make a secret button by placing it inconspicuously behind a smooth surface. For instance you could place them under a nonmetallic card table and by casually pressing the right location on a tabletop surface you could mysteriously control your DIY project.