X10 was developed in 1975 by Pico Electronics in Scotland, in order to allow remote control of home devices and appliances. It was the first general purpose home automation network technology and remains the most widely available.
Household electrical wiring is used to send data between X10 devices. This data is encoded onto a 120 kHz carrier which is transmitted as bursts during the zero crossings of the 50 or 60 Hz AC alternating current waveform. Most inexpensive X10 devices only receive commands and do not acknowledge their status to the rest of the network.
An RF protocol is also defined to allow for wireless keypads, remote switches, motion sensors, etc. The wireless protocol operates at a frequency of 310 MHz in the U.S.
The X10 protocol is relatively slow and prone to power line wiring interference, signal collisions and attenuation which can make it less reliable than other technologies. X10 signals are not encrypted which can also lead to reliability issues.