The abbreviation "ADT" stands for American District Telegraph, which is a security company with a corporate office located in Boca Raton, Fla. The company was originally established in 1867 and was called the Gold and Stock Telegraph Company.
ADT also offers fire protection and other alarm monitoring services in 35 countries worldwide. Serving over 6.5 million customers, it is the largest security company in the United States and Canada. The company holds 13 percent of the market share in small businesses and 25 percent of the residential market share. As of 2013, ADT has two monitoring stations in Canada and four in the United States. ADT officially became a public company in the 1960s.