Mobile devices such as smartphones and music players
have recently become pervasive to the point that many people
carry them at all times. Mobile devices usually incorporate various
sensors, such as GPS sensors, accelerometers, or gyroscopes. For
instance, most Android-powered smartphones have built-in sensors,
and these sensors can be controlled by developers using
Android APIs. Thus, instead of attaching a wearable sensor to the
user’s body, a mobile device can be kept in the pocket of the user’s
pants, which is less bothersome