The disclosure generally relates to synchronizing application account data using out-of-band device-to-device (D2D) communication between peer wireless devices. More particularly, a first device may generate a local unique expression that includes a name, one or more user credentials, and a last update time associated with an application registered for a D2D-based application synchronization service. In response to detecting one or more external unique expressions from one or more peer devices in proximity that match the name and the user credentials associated with the registered application, the first device may then identify, among the one or more peer devices, an update device associated with an external unique expression having a last update time more recent than the last update time associated with the local unique expression and request an update to synchronize the application account data associated with the registered application from the update device over an out-of-band D2D connection.