Examples described herein involve expanding playback of a media item from a first playback device to a second playback device. In one example, a first playback device, while playing a media item as part of a first zone, identifies a second playback device within a proximity of the first playback device, determines that the second playback device is in a second zone, and responsively, causes the second playback device to join the first zone and begin playing the media item in synchrony with the first playback device. In another example, a first playback device of a first zone determines that a second playback device playing a media item as part of a second zone has entered a proximity of the first playback device, and based on the determination, joins the second zone and begins playing the media item in synchrony with the second playback device.