Examples described herein involve expanding playback of a media item from a first playback device to a second playback device. In one example, while a first playback device is playing a media item as 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. The first playback device determines that playback is to be expanded to the second playback device, and transmits a command to cause the second playback device to (i) join the first zone and (ii) begin to play the media item in synchrony with the first playback device.