Xiaomi has yet to expand most of its mobile products to the US market, but it had an unexpected hit on its hands with the competitively priced (and globally available) Mi Band fitness tracker. The $15 device shipped more than 20 million units, and now the follow up Mi Band 2 is official after being shown off a few weeks ago. It's a little more expensive than the last one (RMB 149 or $23), but it has some nice upgrades.

The Mi Band 2 has a small OLED display that can display the time, your heart rate, step count, and more. The last Mi Band only had a few LED indicators. Xiaomi also says it managed to cram a larger battery in the Band 2 for a solid 20 days of use per charge. The accelerometer is used to track steps and sleep, but it can also now alert you if you've been sitting still for too long so you can get up and stretch.

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This is a Bluetooth 4.0 device that can pair with your phone to receive alerts for calls and notifications. Xiaomi also touts automatic device unlocking for Mi phones. If it's a standard Bluetooth connection, the Mi band 2 should work with smart lock on other phones. This is a little unclear. There will be a line of colorful improved band options for the Mi Band 2, and the device itself is IP67 water-resistant.

The Mi Band 2 launches in China on June 7th. The timing for other markets has not been released yet.