In 1853, a man named Edward Callahan was working as a telegraph operator in New York when he came up with an idea: what if a business could send a signal the moment something went wrong? He built a system that connected buildings to a central monitoring station using telegraph lines. If a door was opened or a window was disturbed, a signal went out.

That idea became the foundation for what would eventually turn into ADT—originally the American District Telegraph company. In the beginning, it wasn’t about homes. Banks, warehouses, and rail depots were the customers. Places that had something worth stealing.

And home security didn’t really become a business until much later.

By the 1960s and 70s, the U.S. had changed. Suburbs had expanded quickly after World War II. More people owned homes, and more people had things inside those homes they considered valuable. And crime—at least as people experienced it through news and word of mouth—felt like it was rising.

That’s when companies like Brink's and ADT started pushing into residential markets. To do this, they sent salespeople.

The pitch was straightforward. A rep would knock on your door and ask a few questions: Do you lock your doors every night? Do you travel? Do you have kids? Then they’d walk you through how easy it would be for someone to break in. Sometimes they’d point out a side window or a sliding door. The sale used fear and psychology.

Then they’d offer the solution: a system that connected your home to a central station, staffed 24/7. If anything happened, someone would know immediately and could send help.

The systems themselves were basic by today’s standards—magnetic contacts, motion sensors, and loud sirens. But the real product was the monitoring contract. The companies made money through monthly recurring revenue, decades before SaaS made that model famous.

The in-home demo became a core part of the sale. Reps would show how the alarm triggered, how quickly the signal went out, and how loud the siren was. Some reps carried portable units. Others relied on storytelling— “A family down the street just had this happen…”

It worked because it hit something specific: responsibility.

By buying a security system, you were doing everything you could to protect your family.  

By the 1980s and 90s, the model had scaled. Door-to-door sales teams spread across suburban neighborhoods. Commissions were high, while the barrier to entry was low. Some reps treated it like a career, while others came through for a summer, knocked on a few hundred doors, and left.

At the same time, the technology improved. The systems became more reliable, and monitoring centers expanded to keep up with demand. Branding also got stronger. The ADT sign on the lawn became part deterrent, part status signal. It told people something about you and how you lived.

Then, in the 2010s, companies like SimpliSafe and Ring changed the model once again. There were no contracts. You could install the product yourself. And everything worked off an app on your phone. You didn’t need to deal with a salesperson in your home anymore. You could order everything online in ten minutes.

But there are still reps knocking on doors, especially for bundled offers—security plus solar, security plus smart home packages. The script now is less focused on fear, and more focused on convenience. The structure, however, remains the same: find the gap, make it feel real, and close it.

From a telegraph wire in 1853 to a push notification on your phone—an entire sales industry has evolved.