Examples described herein involve expanding playback of a media item from one playback device to another playback device. In an example implementation, while a first playback device is part of a first zone, the first playback device identifies that a second playback device has moved to a location that is within a given physical proximity of the first playback device. The first playback device determines that playback is to be expanded from the second playback device, and responsively, joins the a second zone that comprises the second playback device and initiates playback of media in synchrony with the second playback device.