United Airlines is buying a stake in the biometric screening company Clear. Clear is a fee-based service that allows you to pass through expedited security at more than 50 airports and sports stadiums.Under the partnership, biometric screening kiosks by Clear are expected to be added at United Air's hub airports such as Houston International, Chicago O'Hare and Newark Liberty. Other United Air's US hub airports, where Clear has already been added, include those in San Francisco, Los Angeles, Denver and Washington, D.C.”Our shared focus on the customer experience will enable us to reduce friction at every touch point and help travelers enjoy more of what they love,” Caryn Seidman-Becker, Clear's Chairman and Chief Executive Officer, said in a statement, cited by CNBC.Clear has steadily expanded its presence since its establishment in 2010 and currently has kiosks for passenger identification at over 30 airports across the United States.Delta Air also owns a stake in the security identity company.