~WHAT IS X10?~
One of the keys to the ease of home automation is the use of a technology called "X10." X10 is not only the name of the company, but it is a standardized communication "language" that allows powerline modules to "talk" to each other through the existing 120 VAC wiring in your home. Simply plug or wire in an X10 compatible module into your AC supply and it can communicate with any other X10 device in your home to give you remote control of virtually any light or appliance. No special costly rewiring is necessary. X10 has been around since the 70's so it is a tried and tested technology. Up to 256 different addresses are available by setting "code wheels" that are "house" codes (letters A thru P) and "unit" codes (1 thru 16). If you want more than one module to respond to the same signal, simply set them to the same address.
Some new devices have done away with the code wheels and allow you to actually "program" the X10 address into them. In some ways this makes the devices more reliable since it is solid state and usually results in a smaller compact version of the device as opposed to one with code wheels.
X10 devices made 20 or 30 years ago (if they're still in working order) generally will work with X10 items made today as the codes that are used to send the signals to communicate are still the same. Most X10 devices made by different manufacturers can be used together as they all use this same communications language or coding. Sometimes a manufacturer may come up with something different in an attempt to "build a better mouse trap" and they will have there own "language." Smarthomes Insteon and Advanced Control Technologies (ACT) A10 for example. Sometimes X10 capability is included with these new signaling devices so that they can be integrated with an existing X10 system so that you don't need to throw it all out and go with all new stuff. If it is X10 compatible, generally it will say so in the items product description. Each manufacturer believes their product is better and it may actually be. But, if a manufacturer wants to ensure a lasting and reliable product line, they will have X10 capability added in so their devices can be used in existing X10 systems. Sometimes they may use only their new "language" so they can restrict you to only buying their product line or product brand thereby "cornering the market." You would do best to avoid any non X10 compatible products since if the company goes out of business or does away with their product line you'll be stuck with a bunch of neat high tech but basically useless junk with no way to add to it or replace things as they go bad.
The most basic X10 system would be a transceiver and a keychain remote. EXAMPLE: Plug a lamp into the transceiver. Set both the house and unit code on the transceiver and the keychain remote to A1. The lamp will now turn ON and OFF via wireless remote control using the keychain remote. There are lamp modules that allow you to dim lamps. There are wall switch modules that wire directly in place of your standard wall switch. Then the lights can be controlled normally at the switch but can also be controlled via remote control. There are modules for appliances both 2 pin and 3 pin grounded, 240 volt modules for heavy duty applications, wireless wall switches, chimes, motion detectors, etc, etc and so on. There are X10 products to suit virtually almost any application. If it is electrically operated and you want to control it via remote, odds are there is a way to do it. Best of all, X10 products can be freely mixed and matched regardless of manufacturer since they use the standardized "communications language" making them all compatible with each other.
Transmitter/Controllers send a specially coded low-voltage signal that is super-imposed over your home's AC wiring. These can be either directly connected to the AC line (plugged or wired in) or wireless (using RF) with the use of a transceiver. A transmitter is usually capable of sending up to 256 different addresses.
Receiver modules "catch" the signals sent by a transmitter. Once a signal comes in that matches the address you have the module set to, the device that's controlled by the module will turn ON, OFF, DIM, BRIGHTEN, etc. Receivers generally have code dials that are used to set the address. Some are solid state that are set by a simple programming sequence.
Transceiver modules receive the RF signals from a wireless transmitter via an antenna, encode it, and then transmit it onto your home's AC wiring. The X10 codes are actually transmitted between the 60hz alternating cycles in the fraction of a second when the voltage is nearly zero. Then they are picked up by a receiver module set to the same address as the transmitter that originally sent the command. Hence the name transceiver, since it is both a transmitter and receiver of X10 signals. Most transceivers also come with a built-in appliance module for even greater versatility.