With the 1975 release of X10, a communication protocol for home automation, the smart home, once a pipe dream a la The Jetsons, came to life. X10 sends 120 kHz radio frequency (RF) bursts of digital information onto a home's existing electric wiring to programmable outlets or switches. These signals convey commands to corresponding devices, controlling how and when the devices operate. A transmitter could, for example, send a signal along the house's electric wiring, telling a device to turn on at a specific time ().
However, as electrical wiring isn't designed to be particularly free from radio-band "noise," X10 was not always fully reliable. Signals would be lost and, in some cases, signals wouldn't cross circuits that were wired on different polarities, created when 220-volt service is split into a pair of 100-volt feeds, as is common in the U.S. Additionally, X10 was initially a one-way technology, so while smart devices can take commands, they cannot send data back to a central network. Later, however, two-way X10 devices became available, albeit at a higher cost.