https://ift.tt/2pDQN5R What external heart rate monitor should you get for your Apple Watch or iPhone? The Apple Watch has an excellent oximeter-based heart rate monitor for tracking your day and basic workouts, but it's not perfect for more endurance or weight-based activities. For one thing, that monitoring comes at the expense of battery life: The smartwatch's health sensors account for a large majority of battery drain; as such, Apple limits how often the sensor records data , even during workouts. At rest, you'll get heart rate data every ten minutes; during a workout, you're likely to get recordings every 10 seconds to a minute. The wrist-based monitor can also get tripped up if you tend to do a lot of exercises involving wrist bending or quick movement — the oximeter works by measuring the movement of your blood using light, and when you flex your wrist, you can momentarily change that circulation, leading to erroneous heart readings. (If you've eve