Worldwide shipments of wearable devices are expected to reach 101.9 million units by the end of 2016, representing 29 percent growth over 2015, according to the International Data Corporation (IDC).The IDC Worldwide Quarterly Wearable Device Tracker sees the market for wearable devices experiencing a compound annual growth rate of 20.3 percent, culminating in 213.6 million units shipped in 2020.By category, IDC sees the market as such:Smart watches: The category is expected to increase from 41 percent of total wearables shipments in 2016 to 52.1 percent in 2020. However, not all watches are the same. While smart watches are in the spotlight today, future growth will come from basic watches that provide some sort of fitness/sleep tracking while not being sophisticated enough to run third-party applications on the watch itself. Traditional fashion brands like Fossil and health/fitness companies like Fitbit and Withings will help this segment grow.Wrist Bands: Through their simplicity, fitness-focused wrist bands have dominated the market thus far. Driven by low cost vendors Xiaomi and giants like Fitbit, this category will remain influential and accessible. However, that dominance will be challenged by watches as many watch vendors incorporate basic fitness features into their products.