When paired with the Aqua Training Bag, the Aqua Training Bag Sensor gives you the most bang for each and every workout. Measure your progress over time, providing real-time data and transparency. The Aqua Training Bag Sensor works exclusively with 21", 18", or 15" Aqua Training Bags. Create a personalized profile, track your daily activity and your workouts, while the sensor provides real-time data to help you measure your speed, force, and progress over time. Take Your Training To The Next Level Link To Your Smartphone Use With The App Track Past Workouts Store Your Personal Data Round-By-Round Analytics Punch Force Hardest Punch Punch Calorie Measurement Punch Frequency Personalized User Experience Punch Power Threshold Round Timer Start/Stop Bell Calorie Counter Requires 2 AAA batteries - that are not included!