Every activity tracker on the market has the same technology: an accelerometer. These devices keep track of up, down, sideways and front-to-back motions. When the accelerometer is still, it doesn’t record anything but gravity; when it’s moved, the accelerometer keeps track of acceleration. My FitBit is basically an extension of my body, but there are still some subtle limitations.
Most people wear their trackers on their wrist like Jared Haftel does in the Vine seen here. The accelerometer keeps track of motion and then determines how many steps you’ve taken, how many calories you’re burning and, overall, how active you’ve been.
Activity trackers also measure your inactivity. This becomes a problem when you’re doing a certain type of “difficult” sitting, such as a wall-sit or yoga – the activity tracker can’t tell the difference between this type of sitting and reclining on the couch. The accelerometer can’t measure exertion, just movement.
Most activity trackers have an accompanying smartphone app that syncs with the device. On the app, you can tell the tracker which type of activity you’re engaging in.
At the moment, activity trackers can’t measure activity when a person’s biking, although you can tell your activity tracker how long you rode a bike for. While there are some kinks to work out, algorithms for determining exertion are improving. Plus, keep in mind that any type of movement (other than lifting countless potato chips to your mouth) can improve your health.