Why we like it: Doing a circuit training program—where you race from exercise to exercise with little to no rest in between—is one of the most effective ways to build lean muscle and burn fat. The problem is having to watch the clock all the time and doing the math to know when to move onto the next exercise. This lightweight, water-resistant workout timer lets you program in two time periods (how long you want to do each exercise for and how long you want to rest in between exercises). As you work out, a horn lets you know when to move to the next station and rest—and when it’s time to start exercising again—so all you have to do is sweat (and not think!).