These watch components sit on top of a substrate that goes against the wear’s skin. Visible here are the vibration motor, OLED display, and Bluetooth antenna, as well as the C-shaped metal brace and clips holding the PCB in place.Īn examination of the Charge internals begins with prying off the watch’s plastic housing to reveal the display, circuit board, and vibration motor (from Jinlong Machinery Electronics in China) used for signaling. The watch internals with case removed look like this. The watch works in conjunction with a smart phone app that reads out all these factors and adds niceties such as badges for making progress toward a fitness goal. It’s said to have a battery life of seven to ten days – considered good for smart watches like this - and can monitor sleep patterns. The watch also syncs with Bluetooth and comes with a charging cable. The Charge tracks steps, distance, calories burned, floors climbed and active minutes, monitors sleep, and has caller ID that can read out incoming calls when your phone is nearby. To get an idea of how fitness watches work their magic, we tore down one of the more popular fitness watches, the Fitbit Charge. The fitness tracking firm Fitbit says it sold something over 21 million fitness watches last year.

Here’s a look at the electronics and sensors deployed inside a widely used fitness watch.

Fitbit charge