Methods, devices, and systems are presented for screen locking or delaying the screen locking of mobile devices, such as smart phones, based on whether the gait of the current user match that of its true, authorized owner. A user's gait can be measured using accelerometers embedded in the device. Other movements, such as where a user normally goes to work, can be measured using GPS or other positional location data and used to lock or delay locking of the screen.