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There had been a lot of small telegraph delivery businesses in the United States in the 19th century. In 1874, 57 district telegraph delivery companies affiliated and became "American District Telegraph". With the enhance in telephone utilization in the late 19th century, adt security systems organization little by little declined in popularity. ADT tried branching out and developing their signaling business whilst still sustaining their telegraph company as primary revenue source. ADT included into Western Union in 1901. ADT separated its messenger company from its principal signaling company at this time. In 1909, Western Union and ADT came beneath the control of AT&T. home security system began to increase into new places such as hearth alarms and burglar alarms between 1910 and 1930, but was stored separate from AT&T's Holmes alarm business. adt became a publicly owned business in the 1960s.

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