Wearable device vendors shipped 78.1 million units this year, more than double last year’s total, which was 28.8 units, according to IDC. 

Fitbit’s shipments in 2015 reached 21 million units and accounted for 26.9 percent market share. Devices from two other wearable device vendors, Xiaomi and Apple, account for about 15 percent market share each. Xiaomi shipped 12 million units and Apple shipped 11.6 units, according to the firm's estimates.

Both Garmin and Samsung accounted for about 4 percent market share each, IDC says, both topping 3 million units shipped, and the other wearable device makers made up the remaining 34.5 percent. In total, wearable device vendor shipments grew 171.6 percent over 2014.

"Triple-digit growth highlights growing interest in the wearables market from both end-users and vendors," IDC Wearable Research Manager Ramon Llamas said in a statement. "It shows that wearables are not just for the technophiles and early adopters; wearables can exist and are welcome in the mass market. And since wearables have yet to fully penetrate the mass market, there is still plenty of room for growth in multiple vectors: new vendors, form factors, applications, and use cases. This will help propel the market further.”

In just the fourth quarter of 2015, global shipments for wearable devices reached 27.4 million. Fitbit devices accounted for almost 30 percent of the market share with 8.1 million units shipped. 

Apple also overtook Xiaomi in Q4 2015. While Apple saw 4.1 million shipments and maintained 15 percent market share, Xiaomi had 2.7 million shipments, which was 9.7 percent of the market share at the time. Following Apple and Xiaomi, Samsung shipped 1.3 million units, Garmin shipped 1 million units, and a number of other wearable device makers shipped the remaining 10.3 million units at the end of last year.

“The market can only get so far with 'me too' and 'copycat' wearable devices,” Ramos said. “End-users expect improvement from what they have now, and new applications to spur replacement and increased adoption. Historical data, like steps taken and calories burned, has been a very good start. Prescriptive data, like what else a user can do to live a healthier life, coupled with popular applications like social media, news, and navigation, will push wearables further, and attract more users.”

Yesterday, in Fitbit’s Q4 2015 earnings call the company reported that it had sold 21.4 million devices in 2015 and added 18 million new registered device users, last year. Specifically in the fourth quarter last year, Fitbit’s revenues reached $712 million, up 92 percent from the fourth quarter of 2014. These revenues were driven by three of the company’s newest devices, the Charge, Charge HR, and Surge, which accounted for about 79 percent of the company’s revenue.