The Fitbit Tracker  uses a three-dimensional acelerometer similar to that in the wii to sense user movement. The Tracker measures steps taken, and combines it with user data to calculate distance walked, calories burned, floors climbed(no ofSTAIRS), and activity duration/intensity. It uses an OLED to display this and other information such as the battery level. It also measures sleep quality by tracking periods of restlessness, how long it takes the wearer to fall asleep, and how long they are actually asleep.