Callahan created an emergency call box that serviced fifty of his neighbors. Callahan’s system was designed to alert other neighbors by assigning a certain number of rings for each house that would signal others. For example, if an alarm rang in house A, houses B, and C were notified. In addition, Callahan expanded his idea by dividing New York City into districts that would be connected to a central monitoring system. In the event of an emergency, a messenger boy was sent to arrange for help in a particular district.

Furthermore, the emergency boxes invented by Callahan are still utilized today for police, fire, and messenger services. Callahan utilized the idea of obtaining help in the event of an emergency to form the American District Telegraph (ADT) in 1871 which has become largest security company nationwide today. However, ADT is currently facing numerous lawsuits because they knowingly failed to inform customers of the possibility their system is not encrypted and easily hacked.

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