Apple, a $642 billion (£424 billion) company, is being beaten by Fitbit, a $6 billion (£3.9 billion) company, according to data from research firm IDC.
Fitbit, which predominantly makes fitness trackers, saw sales of 4.7 million units while Apple, which makes the Apple Watch, shipped 3.9 million units. Both companies are up from a year ago when Fitbit sold 2.3 million devices and Apple sold zero.
The total wearable industry grew almost 200% with sales rising from 7.1 million units to 21 million units.
Xiaomi, the Chinese startup, saw sales of 3.7 million wearable devices (up from 400,000 in the same period last year) while Garmin, the Swiss outdoor fitness company, saw sales of 900,000, up from 500,000 in the same period.
Fitbit recently launched its corporate wellness service, which is now used by 70 Fortune 500 companies. The initiative aims to get employees fitter and more productive. The Apple Watch also offers a feature that encourages users to stand up and walk around.
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