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You never forget how to ride a bike — but sometimes you forget how fast and how far you pedaled. Therein lies the beauty of the Wahoo Fitness Blue SC, a Bluetooth 4.0 bicycle sensor that transforms your iPhone into the ultimate cycling computer, allowing you to record all your workout data, from pace, cadence and location to calories burned. A built-in odometer also tracks lifetime mileage, displaying the information by week, month or year.

$60, www.wahoofitness.com