ADT is the largest security company in the United States. It has approximately 5 million customers, and has been in business since 1874. ADT is worth approximately $4.2 billion.
ADT is an integrator, which means that they specialize in purchasing equipment produced by other companies, and integrating them together. This allows them to have a wide range of product offerings, however they tend to have some compatibility issues because of the communication problems between devices of different manufacturers.