Workout round lengths can be adjusted to 2 or 3 minutes, rounds from 1 to 12 and rest time between rounds from either 30 or 60 seconds. An audible bell sound and/or vibration feature alerts athletes to the start and end of each round. Can be worn securely around arm with elastic band provided, clipped to shorts or stand alone. Personal 3" x 2" x 1.25" size is ideal for every level athlete from beginner to professional. Requires 3 AAA batteries included.