The American District Telegraph (ADT) is a company that provides security and alarm monitoring services. Founded in 1874, it originally focused on telegraph services but later shifted its focus to the security industry. ADT is known for its residential and commercial security systems, including burglar alarms, fire alarms, and surveillance cameras. Over the years, ADT has grown to become one of the largest security companies in the United States. It offers a range of services, including 24/7 monitoring and smart home integration. The company is a subsidiary of Tyco International, which is part of Johnson Controls International.