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Xiaomi’s incredibly successful Mi Band has a successor that’s much more intelligent yet still amazingly affordable. It’s called the Mi Band 1S, and it’s capable of tracking your sleep, has a built-in heart rate monitor, and costs just $21.

Xiaomi isn’t the only company offering affordable fitness trackers now, but you usually have to pay a premium for features like heart-rate monitoring. But not with the new Mi Band 1S, which will make its debut ...