Till January of this year, the Wahoo Key for iPhone ($80) dongle pwned fitness on the iPhone. Why? Because the tiny, ubiquitous dongle gives the iPhone access to dozens of ANT+ sensors, and more fitness apps than any other system — turning your iPhone into a fitness-tracking powerhouse.
Then in January, Wahoo one-upped itself and introduced the Wahoo Blue Bluetooth heart-rate strap, which completely bypasses ANT+ and instead communicates via low-energy Bluetooth v4.0. Does this mean the Key is obsolete? Not by a long shot..