When you tilt a smartphone, gravity shifts microscopic silicon fingers inside its accelerometer by only a few nanometres, changing the capacitance between them and producing the electrical imbalance the phone reads as a new direction for down
Every smartphone contains a silicon structure smaller than a grain of rice that senses gravity by measuring how far a comb of tiny fingers moves when you tilt the device. The distances involved are a few nanometres — smaller than a strand of DNA.