Tim Whall
(Chief Executive Officer)
Jeff Likosar
(Chief Financial Officer)
Jim DeVries
(President)
Dan Bresingham
(Chief Administrative Officer)
P. Gray Finney
(Chief Legal Council)
Jamie R. Haenggi
(Chief Sales & Marketing Officer)
Bob Dale
(Senior VP, National Account Sales)
Donald Young
(Chief Information Officer)

The ADT Corporation is an American corporation that provides residential and small business electronic security, fire protection, and other related alarm monitoring services in 35 countries. The corporate head office is located in Boca Raton, Florida. In February 2016, the company was acquired by Apollo Global Management for $6.9 billion in a leveraged buyout.

In 1863, Edward A. Calahan invented a stock ticker and formed the Gold and Stock Telegraph Company in 1867 to exploit the technology. Gold and Stock also developed a messenger system that sent instructions to and from the stock exchange floor. Three years later, the president of Gold and Stock Telegraph Company woke up to a burglar in his home, which inspired him to create a telegraph-based alert system. This system eventually connected 50 of his neighbors to a central station where all the alert boxes were monitored. There were many small telegraph delivery companies in the United States in the 19th century. In 1874, 57 district telegraph delivery companies affiliated and became "American District Telegraph". With the increase in telephone usage in the late 19th century, ADT's messenger business slowly declined in popularity. ADT tried branching out and developing their signaling business, while still maintaining their telegraph business as primary income source. ADT incorporated into Western Union in 1901 and separated its messenger business from its main signaling business at that time. In 1909, Western Union and ADT came under the control of American Telephone & Telegraph Company (AT&T). ADT began to expand into new areas, such as fire alarms and security alarms between 1910 and 1930, but was kept separate from AT&T's Holmes alarm business. ADT became a publicly owned company in the 1960s.

In 1964, ADT was found to be a monopoly in restraint of trade. It was shown to provide almost 80% of the central station alarm service in the United States. In some cities, such as New York City and Memphis, Tennessee, they were the sole provider. They were also found to have forced competitors out of business by lowering prices below cost. They would charge national accounts very low prices in cities with competitors and much higher prices where no competition was available. ADT was forced to adopt a national price list, which could not be varied, to help establish central station competitors in cities without competition, and to pay fines and triple damages to the federal government, customers, and local competitors.

In the early part of 1987, the firm of Hawley Goodall, owned by Lord Ashcroft, bought the Indianapolis-based Crime Control Inc., the fourth-largest company in the U.S. security market, for $50 million. Later in the year, it bought ADT and moved to Bermuda. This purchase transformed Hawley into the leading security services business in the United States, and resulted in the majority of its revenues coming from the North American market. As a result of the acquisition, Hawley changed its name to ADT Limited and decided to refocus its business around security services. At the end of 1987, the company sold its North American–based facility services business to Denmark's ISS A/S.

In 1997, ADT was purchased by Tyco by means of a reverse takeover. In May 2010, ADT acquired competitor Broadview Security for $2.0 billion and transitioned services to ADT. On September 19, 2011, Tyco announced that it would split into three companies, ADT being one of the three. On October 1, 2012, ADT debuted as an independent public company and began trading on the New York Stock Exchange (NYSE: ADT). In 2014, it acquired the Canadian company Reliance Protectron Security Services.

In early 2010, Tyco International announced that it was acquiring Brink's Home Security Holdings, (operating as Broadview Security) and was merging the company with its ADT brand name in a transaction valued at $2.0 billion. The transaction, which was finalized and closed mid-2010, combined the #1 and #2 security companies in North America, adding Broadview's 1.3 million customer accounts and $565 million in annual recurring revenue to ADT's existing customer base of 7.4 million accounts and $3 billion in annual revenue.

In February 2016, Apollo Global Management acquired ADT for nearly $7 billion and intends to merge it with another home security firm, Protection 1. The purchase price represents a premium of approximately 56 percent over ADT’s closing share price on February 12, 2016 and, when combined with Protection 1, represents an aggregate transaction value of approximately $15 billion.

ADT is the largest security company in the United States and Canada, serving over 8 million customers. As of 2013 ADT holds 25% market share of the residential market and 13% of the small business market in the US. ADT maintains five monitoring stations in the United States and one in Canada.

ADT has an authorized dealer program. Under this program, independent dealers offer security system installations which are then monitored by ADT. Some ADT Authorized Dealers use similar DSC, Honeywell/Ademco products as installed by ADT, while other dealers utilize GE or ITI products.

Whether a customer purchases ADT monitoring services directly from ADT or through an authorized dealer, a monitoring contract is required.