X-10 was a company that made a set of remote control electrical devices using the power lines for transmission of the remote messages. The transmission protocol was licensed to other companies and became a very common (within the small home automation area) method for operating line items via remote and computer control. The system was not robust enough for critical items since it was possible for interference to cause some signals to be lost or to trigger accidentally. If your door doesn't lock because of interference, it is bad. If your stove turns on because of interference, it could burn your house down.
They also made (at a later time) some surveillance and alarm items that could be used independently or slightly connected (triggering other items to turn on when a door is opened) to the remote system.
I doubt that anyone would call it a significant security system because it would be too easy to defeat. However, the sensors can do things like turn on your bathroom or stairs lights as someone enters the area and automatically turn them off after they leave.
X-10 is a protocol for controlling devices (e.g. lights, coffee pots, TV sets, etc.) over power lines in a house. It is far from an all-in-one system. I bought a number of controllers and modules to control stuff from Radio Shack in the 1980's. Some of the newer features I may not be aware of.
Some modules replaced light switches. Some modules plugged into outlets and you then plugged the lamp or appliance into it. Appliance modules didn't have dimmers and generally had more power capacity. I believe there were some modules that replaced outlets.
There are a variety of controllers. Some are intended to sit on a chair or table. Some do timed control of the devices on a schedule. Some are interfaced to a computer. Some later devices like thermostats or motion-detectors could be programmed to send commands to modules under certain conditions.
Each module has a setting for a "house code" and "unit code". There are 16 of each. In theory, a house (or apartment) used 16 or less of these and a nearby house used a different house code to avoid (non-malicious) interference. Of course, there's nothing to prevent a given house from using more than one code. Two devices that are supposed to be controlled together may have the same house/unit codes. Some of the manual controllers are a bit awkward to change between house codes frequently. (It's possible, but not very convenient).
You can have an X-10 system with one module and one controller.
The protocol allowed you to select a device, then send it a command, which included: ON, OFF, DIM, BRIGHT, ALL LIGHTS ON, and ALL OFF. The modules intended for lamps, such as ones that replaced light switches or lamp modules that plugged into outlets, had dimmer capability. You sent repeated DIM or BRIGHT commands to adjust the level. A module knows whether it's supposed to be controlling a "light" or an "appliance" (dimming an appliance is not a good idea). ALL OFF is to turn everything off when you go to sleep. ALL LIGHT ON is to turn all the lights (not appliances) on when you hear a burglar.
There is no acknowledgement in the protocol (at least when I was using it, long ago). You don't know you are commanding a module with the wrong code. If interference jams the signal (certain printers with switching power supplies and my electric razor did that. Also, some people had trouble if the controller and module were on different phases of the power line), you don't know it didn't work. You can also turn on devices manually (turn the appliance or lamp switch off then on). Nothing is notified of this, so you may run into the situation of the computer or timed schedule not knowing the correct state of the device, because of manual operation or operation of a manual controller.
Unfortunately it is also the name of a company that peddles cameras and security systems etc. that are unrelated to X10 power line control, and I guess that may be a major part of what is confusing the OP.
This is a very old protocol, as other person said it was designed in the early 80's.
x10.com started off selling x10 parts, and they still do, buried in the website, if you search for x10 appliance, x10 controller, x10 lighting on their site you'll find it. I only used x10 for one device, an air conditioner plugged into an appliance module, controlled by another x10 device attached to a thermostat, and it would work. If you want more elegant control, better quality devices do a search on Zwave, Insteon, UPB. Of course these options are a lot more expensive. If all you want is a quick cheap solution in something non-critical then X10 can still be the way to go. Ebay is a great place to pick up new X10 devices really cheap.
I have a whole home wired for X10 using mostly Leviton parts. Everything works fine and it was no cheaper than using any other protocol. The big benefit and reassurance is multi-vendor support and sourcing. If Leviton or another major supplier was ever to offer the parts I use in a better and multi-vendor supported protocol I'd be willing to switch. One part I have found impossible to match is the X10 compatible HXC4D which is the 4 device dimming wall switch controller.
X10 is an incredibly primative and low performance communications system that operates over power lines at the zero crossing. It's good for 60bps, or about a full second for a single command. It's original spec is open loop, permits 16 devices, 16 house codes, and commands to turn on on or off all or one of 16 devices.
It has been enhanced over the years with such features as status reporting and using multiple house codes to permit more than 16 devices, and proprietary multicommand sequences to get around some of its limitations.
I laughed for 15 years when my 300watt halogen came on work day mornings and brightened over the period of an hour to wake me up gently for work each day.
It didn't work very well because it never did it on weekends or statutory holidays for some reason and the damn light would blink five times if I didn't get up at the critical time for getting to work. Damn thing knew I was still in bed, somehow. The kitchen sink light would start to blink if I was still in the kitchen at the critical "get-in-the-car" time also. Must have been defective or something.
My deck lights used to flash if somebody came to the front door or walked around the side of my house too. I was glad not to get caught nude sunbathing by family and visitors but that thing was a joke too.
X10 is still around because it is good value home automation. There are more reliable systems, but at five times the cost. I have over 100 X10 control points and have 95% command reliability which isn't bad for the investment price. Also Smarthome.com offers 2-way modules reporting back a status change, so system can be closed loop if desired. X10 has been around since
1979 and is l>>By what I gather, it appears to be an all in one package or system which