Smart homes of the future will automatically adapt to their surroundings using an array of sensors to record everything from the building’s temperature and humidity to the light level and air quality.

If these walls had ears, they might tell a homeowner some interesting things. Like when water is dripping into an attic crawl space, or where an open window is letting hot air escape during winter.

Using a home's electrical wiring as a giant copper antenna allows for wireless sensors that can communicate over a whole house and run for decades on a single watch battery. The device could be used ...