The "one more thing" at the Xiaomi MI4 launch was the Mi Band, the Chinese company's first smart wearable, and it's obviously aggressively priced: Just CN¥79 or about $13! Like many of its competitors, the Mi Band tracks your movement (walking or running) plus sleeping pattern, and you can also use it as a smart vibrating alarm to wake up feeling better. Interestingly, a single charge on this waterproof device will last up to 30 days, which easily beats it competitors that tend to last for a week or less. Better yet, the band doubles as a security token that automatically unlocks your phone -- likely just Xiaomi's for now -- when within proximity. There's no word on availability just yet, but as always, Xiaomi will likely be debuting this in China where it'll instantly sell out. We've got a couple more product shots -- one of which shows the more stylish bands -- after the break.