X10 is a communications "language" that allows compatible products to talk to each other using the existing electrical wiring in the home. Most X10 compatible products are very affordable and the fact that they talk over existing wires in your home means that no costly rewiring is necessary. Installation is simple, a transmitter plugs (or wires) in at one location in the home and sends its control signal (on, off, dim, bright, etc.) to a receiver which plugs (or wires) into another location in the home.
Using simple dials or buttons you assign each product with one of up to 256 addresses. All X10 compatible products can be freely mixed and matched.
Most of the time, X10 products work without any problems. However, because X10 products talk over your home's electrical wires they may have difficulties in two situations. The first is when there is an appliance running that generates "noise" onto the powerline. Appliances that may cause problems are motors (e.g. dryer, treadmill, vacuum cleaner, etc.) and advanced electronics (e.g. switching power supplies on some laptops, some big screen TV's, etc.). The good news is that all you need to do is plug the appliance into a noise filter.
Advantages
- Inexpensive
- No new wiring is required -- perfect for retrofit
- Simple to install
- Great number of compatible products
- Control up to 256 lights and appliances
- Time proven -- it has been around for over 30 years
Multidomo
At this time Multidomo Networks! support the CM11 PC interface (USB and RS232). Now we are working to support the CM15 USB interface.
X10 it is the cheaper way to try Multidomo. We recomend
1 CM11 (PC interface) 
1 or more LM12 (light appliance)
1 or more LM15 (light appliance) 
1 TM13 (RF receiver) 
1 MS13 (RF motion sensor) 
All this kit cost less than 190€
Where to buy it?
We recommend these online stores http://www.multidomo.com/Shops.aspx