Alphabet Inc.'s Google /zigman2/quotes/202490156/composite GOOGL -1.66% /zigman2/quotes/205453964/composite GOOG -1.67% plans to acquire Fitbit Inc. /zigman2/quotes/202323205/composite FIT -0.16% for $2.1 billion, the companies said in a Friday release. Fitbit shares are up 17% in premarket trading. The deal is expected to close in 2020. Fitbit's stock surged 31% Monday after a report said that Alphabet had made a buyout offer and climbed another 7% in Tuesday's session. "With Google's resources and global platform, Fitbit will be able to accelerate innovation in the wearables category, scale faster, and make health even more accessible to everyone," Fitbit Chief Executive James Park said in a release. The deal comes during a rough few years for the maker of wearables, which has come under pressure amid competition from Apple Inc.'s /zigman2/quotes/202934861/composite AAPL -1.60% Apple Watch. Shares were up 24% on a year-to-date basis as of Thursday's close, compared with a 21% rise for the S&P 500 /zigman2/quotes/210599714/realtime SPX -0.84% , but they were off about 70% from their 2015 initial-public-offering price of $20.