ADT

The Adt Corporation

One of the world's largest home-security companies, ADT monitors alarms, cameras, and smart devices (including Google Nest products) for households and businesses across the US. The name ADT stands for American District Telegraph, born in 1874 after a telegrapher named Edward Callahan was inspired by a nighttime break-in at his boss's home to invent a telegraph "call-box" system linking 50 neighboring houses to a central office. The company began as a messenger service and grew into the electronic alarm and monitoring giant it is today.