“We wanted to make it obvious for everyone who came by,” he said.

He had to pay for that simplicity, though. The total cost of Mr. Weeks’s configuration, including equipment and installation, was $4,600, in addition to the television, which he bought separately.

Mr. Weeks’s bill is representative of current prices; professionally installed smart-home systems run from a few thousand to tens or even hundreds of thousands of dollars, depending on the scope of the job. But Dave Pedigo, senior director of technology for the Custom Electronic Design and Installation Association, a trade group of home theater and home automation installers, said prices for custom automation kept falling, and that one major reason was the advent of touch-screen devices like the iPhone and iPad.

“The onslaught of Apple and Google devices has really been changing this market,” Mr. Pedigo said.

To illustrate Mr. Pedigo’s point, and to give me a taste of what less-affluent homeowners might be able to enjoy in coming years, Mr. Stearns took me to a sprawling house in the Bay Area suburb of Atherton, where his firm had installed an extensive home-automation system.

It included more than a dozen televisions, among them a 103-inch screen in a dedicated home cinema, as well as a whole-home audio system, with speakers mounted invisibly in the ceiling. There was also an integrated lighting and climate-control system, so that the family could, say, keep tabs on the temperature in the wine cellar while working out in the home gym, on the other side of the property.

Here is where the story gets back to the rest of us: This family commands its princely system, which cost $400,000 to design and install, from something as simple as an iPad (or, in this case, any of the seven iPads conveniently located in various parts of the house). Before the advent of touch-screen phones and tablets, Mr. Stearns said, he would have used custom-made controllers for this automated system — and those devices cost several thousand dollars each. But the iPad controller costs $499, a big savings. And because the iPad can be customized with different apps, it can be made to control lots of companies’ systems.

In this way, as prices fall at the high end, they become more approachable for the rest of us. Consider a very basic security and home-automation service offered by a company called Vivint. The professionally installed package carries a base price of $200, and a monthly service fee of about $70, including security monitoring.

To be sure, Vivint’s system lacks the refinements of a higher-priced custom system installed by a dealer affiliated with Mr. Pedigo’s association; Vivint’s system does not plug into a home-entertainment center, for example. But for many people a simple system can be very helpful. Vivint’s includes a video surveillance camera, an automatic door lock, a remote-controlled smart thermostat and a module to control one appliance. (Extra modules cost a one-time fee of $39 each.)