United Technologies Corporation is a worldwide technology company with a long history of pioneering advancements in aerospace, aviation, helicopter design, climate control, elevator design and hydrogen fuel cells. It is a diversified company with a number of products that include Carrier heating and air conditioning systems, Hamilton Sundstrand aerospace systems and industrial products, Otis elevators and escalators, Pratt & Whitney aircraft engines, Sikorsky helicopters, UTC Fire & Security systems and UTC Power fuel cells. In 2005, the company was ranked among the top 20 largest manufacturers in the United States and was in the top 70 largest publicly held manufacturers in the world by Industry Week magazine. Headquartered in Hartford, Conn., United Technologies Corporation employs more than 220,000 individuals. United Technologies Corporation maintains a location in Washington, D.C.