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Heart rate is great for gauging effort during exercise, but wrist-based optical sensors can be thrown off by everything from skin color to the weather, and chest straps—generally considered the gold standard in tracking—can be uncomfortable. COROS’s solution is an armband that still uses an optical heart rate sensor like a watch. But because there’s more blood flow where it’s strapped—on your bicep—it avoids accuracy issues caused by the lack of deep tissue at the wrist. Across thousands of test runs, the Bluetooth-compatible device “measured within three beats per minute [compared to] a chest strap,” says COROS co-founder and CEO Lewis Wu.

Buy Now: COROS Heart Rate Monitor on Amazon

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