The Sony Smart Tennis Sensor SSE-TN1 is a small Bluetooth-enabled sensor that attaches to the butt cap of compatible tennis rackets to analyze your shots and swing mechanics. Works with smartphone app on iPhone and Android to track data like: Ball speed Swing speed Ball spin Impact location on the strings Shot type (forehand, backhand, volley, serve, smash, etc.) The sensor could operate in: Live Mode — real-time stats during play via Bluetooth Memory Mode — stores data internally and syncs later