This application is a continuation of patent application Ser. No. 15/628,946, filed Jun. 21, 2017, which claims the benefit of provisional patent application No. 62/474,533, filed Mar. 21, 2017, both of which are hereby incorporated by reference herein in their entireties.

This relates generally to electronic devices, and, more particularly, to systems that include multiple electronic devices.

Electronic devices such as cellular telephones are often used in isolation. For example, a user may present a video or book on the display of a single electronic device. Using devices in isolation can be unsatisfactory. For example, devices that operate independently are not able to help each other when presenting a video or book to a user.

Multiple electronic devices may be used together in a system. The electronic devices may use sensor measurements and other information to detect when an edge of a first device is adjacent to an edge of a second electronic device. In response to detection of adjacency between the edges of the first and second devices, the devices may transition from an independent operating mode in which each device operates separately to a joint operating mode in which resources of the devices are shared. In the joint operating mode, images may extend across displays in the devices, speakers in respective devices may be used to play different channels of an audio track, cameras and sensors in different devices may be used in cooperation with each other, and other resources may be shared.