Fitbit is still the biggest wearable device maker in the world, but its share of the industry is dropping. A report from IDC shows Fitbit shipped 21 million units in 2015, which is up from 10.9 million in 2014. That's a significant increase, but it comes alongside bigger increases from competitors.

While Fitbit experienced close to 100% annual growth, Xiaomi reported a nearly 1000% jump from 1.1 million units to 12 million. Those shipments gave Xiaomi a 15.4% share of the market, whereas Fitbit has 26.9%, which is down from 37.9%.

The major fluctuations in market standings come from the fast growth of the wearable market as a whole.

Apple came in third during 2015 with a 14.9% share and its shipments were for just one device, the Apple Watch.