A mobile device can communicate with a wearable device to automatically detect when a stowed mobile device becomes unstowed and/or when a mobile device that is in use become stowed. Detection of stowing or unstowing of the mobile device can be based on comparison of data from sensors such as proximity sensors, motion sensors, and/or other environmental sensors between devices. When unstowing is detected, the mobile device can prepare itself for use based in part on context information provided by the wearable device, e.g., by activating a user interface component and/or launching an app based on the context information. When stowing is detected, the mobile device can inactivate a user interface component.