Some 21 percent of US adults use a wearable device right now, and of those, 36 percent use a Fitbit device, according to a Forrester Research survey of 952 online US adults.

After Fitbit, 16 percent use a Nike+ FuelBand, 16 percent use an Apple Watch, 13 percent use Samsung Galaxy Gear, 11 percent use a Microsoft Band, and 10 percent use a Jawbone device.

Forrester also broke out the age demographics of wearable device users.

Of the 21 percent that use a wearable device, 34 percent are Gen Z, aged 18 to 26; 35 percent are Gen Y, aged 27 to 35; and 18 percent are Gen X, aged 36 to 49. Just 11 percent are young boomers, aged 50 to 59, while 7 percent are older boomers, aged 60 to 70, and another 7 percent are seniors, aged 70 and older.

Forrester found that, not surprisingly, the Gen Z generation has the lowest buying power, yet this group has the highest interest in wearables of the other age groups. And although a third of Gen Zers are using wearables, adoption is still lower than that of Gen Yers. Some 41 percent of Gen Zers said they'd consider buying an Apple Watch if the price was right.

Of all age groups, the Gen Yers use the most devices, on average, 4.5 devices each and 35 percent expect to buy a fitness wearable device in the next year. About 8 percent have an Apple Watch, 8 percent have Google Glass, and 11 percent have a Fitbit.

The 70+ group uses technology the least. Just 7 percent of this group use emerging technology, a category that includes wearable devices.