Guests arriving at the Aloft Hotel in Manhattan or one in Silicon Valley will soon be able to do something hotels have dreamed about offering for years: walk past the check-in desk and enter their rooms by using a smartphone as a room key.

The boutique hotel brand from Starwood Hotels & Resorts Worldwide Inc. plans to offer this feature at two hotels, in the Harlem neighborhood and in Cupertino, Calif., before the end of the quarter.

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