A system and method for authenticating users of a digital device includes an authentication device attached to an authorized user. The authentication device includes one or more motion sensors and acts as a user identity token. To authenticate with a digital device, the user performs one or more interactions with the digital device using the hand associated with the authentication device. The digital device correlates the inputs received due to the interactions with the user's hand and/or wrist movement, as measured by the authentication device. Access to the digital device is allowed if the inputs and movements are correlated.