About 4 in 10 U.S. adults (39 percent) aged 18 to 29 say they are online almost constantly, according to a recent survey from Pew Research Center.

Americans aged 30 to 49 have similar habits — with 37 percent online almost constantly. By comparison, just 17 percent of 50- to 64-year-olds and 8 percent of those 65 and older are in a near-perpetual state of internet connectedness.

Smartphones and other mobile devices increase the frequency of internet use, with 31 percent of mobile device users saying they are online almost constantly, compared to just 5 percent of those who go online but not with a mobile device.

Overall, more than a quarter of Americans (26 percent) are online almost constantly. Besides young adults, other demographic groups that are more likely to be online almost constantly include black Americans (37 percent); individuals with incomes of $75,000 or more (35 percent); college graduates (34 percent); and urban dwellers (32 percent).