Abstract. This paper introduces "SyncTap", a user interface technique for making a network connection between digital devices. When a user wants to connect two devices, he or she synchronously presses and releases the "connection" buttons on both devices. Then, multicast packets that contain press and release timing are sent to the network. By comparing this timing with locally recorded one, both devices correctly identify each other. This scheme is simple but scalable because it can detect and handle simultaneous overlapping connection requests. It can also be used for making secure connections by exchanging public keys. This paper describes the principle, the protocol, and applications of SyncTap.