ABSTRACTThe inherent weakness of typical mobile device unlockingapproaches (PIN, password, graphic pattern) is that theydemand time and attention, leading a majority of end usersto disable them, effectively lowering device security.We propose a method for unlocking mobile devices byshaking them together, implicitly passing the unlocked statefrom one device to another. One obvious use case includes alocked mobile phone and a wrist watch, which remains unlocked as long as strapped to the user’s wrist. Shaking bothdevices together generates a one-time unlocking event forthe phone without the user interacting with the screen. Weexplicitly analyze the usability critical impact of shaking duration with respect to the level of security. Results indicatethat unlocking is possible with a true match rate of 0.795and true non match rate of 0.867 for a shaking duration asshort as two seconds.