The ears pick up IR signals from transmitters throughout DCA (and soon in DL, too). Disney Parks Blog says that the ears only sync to WOC within Paradise Park, but there are transmitters in Cars Land (at Flo's, Cozy Cones, Luigi's, traffic light) and at Mad T Party. The new transmitters are at Fantasmic! in DL.
So they won't sync to music at your house, for example. But the lights will blink as long as the battery works (up to 8 hours on average). And if more than one person has the ears, they can be synced together by touching the ears together.