Seed Grove Switches Range - Seeed Studio 101020025, Seeed 101020025 Grove - Tilt Switch is the equivalent of a button which has a two ball type single direction tilt sensitive trigger switch.
Inside the tilt switch is a pair of balls that make contact with the pins when the case is upright.
Tilt the case over and the balls don't touch, thus not making a connection.
It is wired to the SIG line and is used as a digital input.
Seeed 101020025 Grove - Tilt Switch