If you were to strip the rubber coating off the UP, you would find a strip of steel springs that keep the wristband's shape. Mounted on the strip are the UP's electronic components. These include a lithium-ion battery, a motion sensor and a vibration motor. On one end of the steel spring you'll find the 3.5-millimeter jack. On the other end is a button that lets you change the UP's mode of operation.
The battery provides the power and can last several days. Recharging requires you to plug the UP into a USB cable with a headphone-jack adapter.
The motion sensor detects changes in acceleration. Acceleration has two components: speed and direction. If an objection in motion experiences a change in either speed or direction, it has a change in acceleration. Motion sensors detect these changes through tiny electromechanical elements.
A basic solid-state accelerometer looks like a sandwich. The outer layers are capacitance plates carrying an electric charge. In between the plates is a weight suspended between them. When the entire sensor is still, the weight rests between the two plates. But in motion, forces act on the weight, which will move toward one plate and away from another. As the weight draws closer to one plate, its capacitance increases. The other plate experiences a decrease in capacitance. The sensor registers this as movement.
As you move over time, the weight continues to shift, causing more changes in the capacitance of the plates in the sensor. The sensor analyzes the data and converts it into information useful to you, including how many steps you've taken and an estimation of the number of calories you've burned.