The Home Automation Zone

X10 is a communications protocol that allows you to control lights, appliances, thermostats and other devices in your home that are connected to X10 modules that receive signals over your home's AC power lines. Control of the devices is achieved via wireless remotes, hardwired remotes, security systems and even computer interfaces for both PC and Mac. The flexibility provided by the many receiver modules and controllers on the market make X10 a fairly easy and inexpensive way to automate your house without running additional wiring through the walls. X-10 (USA) manufactures several wireless security systems that use X10 wireless technology ; in addition, there are other hard-wired security systems on the market that can utilize X10 technology to control lights, sirens, etc. when various conditions exist.
To avoid confusion, X10 refers to the X10 communications protocol while "X-10" is a trademark of X-10 (USA) Inc. X-10 (USA) Inc manufactures X10 compatible components under the "X-10 Powerhouse" brand name, in addition to OEM manufacturing X10 compatible modules under other labels (Radio Shack, IBM and others). There are other companies that produce X10 compatible equipment, such as Leviton manufacturing, which sometimes provide additional features or heavier-duty modules that are not available elsewhere.

What can it do?
The capabilities of an X10 system are only limited by your imagination. In the simplest cases of incandescent light control, X10 lamp modules provide the capability to turn lamps and hardwired light fixtures on and off as well as providing a dimming function - All by remote control. The remote controls available are widely varied. They include simple remotes that can control up to 16 X10 modules, universal remotes which will control your audio/video system (6 or 8 devices) along with X10 modules, infrared motion sensors, key chain remotes among others. 
Possibly one of the more exciting aspects, however, is the capability for computer control from an interface connected to your PC. The interface includes software which allows you to program events to happen at certain times (i.e. sundown) which are downloaded to the interface, which will operate independently from the PC when the PC is turned off. In addition, the interface will allow you to create macros - for example, a motion sensor could detect when you came in the room, send a signal to the computer interface which would then turn on the lights to 50% brightness and turn on your stereo. The possibilities are endless. The computer interface can even learn your habits (for lighting), then when you go on vacation, you can set it to make the house look lived in using authentic living patterns - no more of those little mechanical timers.

The Technology
X10 communicates between transmitter and receiver modules using Radio Frequency (RF) signals transmitted over the existing AC wiring that carry digital information. The RF signals must be generated by a module or controller plugged into the AC power. This means that the wireless controllers (transmitters) available are not directly sending an X10 signal to the receiver modules; instead, a transceiver module is plugged into the wall that has an antenna that receives the over-the-air RF signal from the wireless controller, then translates the signal into an X10 signal and transmits the signal over the house wiring.