Interval training can help you burn calories and fat in a shorter period of time. You are going to need a decent stopwatch or timer to keep your workout on track though. The Gymboss Interval Timer has you covered. It is a compact interval timer with built-in stopwatch and clock feature. It is useful for HIIT, cardio, CrossFit, weight training, boxing, and other workouts. Sets you back under $20 at this time.