ADT

Adt Inc.

A provider of security and smart home systems for homes and small businesses, ADT offers both professionally installed and do-it-yourself setups, all tied together through its ADT+ app. The name comes from the American District Telegraph, a call-box system telegrapher Edward Callahan invented in 1874 after his boss's house was burglarized — he wired 50 neighbors to a central office so pulling a lever would summon help. Today it monitors around six million subscribers from six UL-listed centers.