Consumers’ enthusiasm for wearable devices may be slowing, reports marketing research firm eMarketer. In October 2015, it forecast wearables usage to climb 60 percent in 2016. It has since revised its expectations for the year, and now expects the category to grow by a more modest 24.7 percent, as interest, particularly in smart watches, slows.

eMarketer expects 39.5 million U.S. adults to have used a wearable at least once a month in 2016. This is well below the 63.7 million users that it had previously predicted. Wearables’ market penetration is forecast to reach 15.8 percent in 2016 and 21.1 percent in 2020.

“Before Apple launched its watch, fitness trackers dominated the wearables space, and consumer surveys consistently found that tracking health and fitness was the main reason people were interested in wearables,” says eMarketer Analyst Cathy Boyle. “They also reported high price sensitivity. Without a clear use case for smart watches—which have more features than fitness trackers, but significant overlap with smartphone functionality—the more sophisticated, expensive devices have not caught on as quickly as expected.”

Wearables have made the most headway among younger consumers. In 2017, eMarketer expects 30 percent of consumers between the ages of 18 to 34 to use them, compared to 17.6 percent of the general population. Their popularity is also skewing along gender lines. While early adopters were primarily male, by 2018 most users are expected to be female as fitness trackers drive the category’s growth.