These devices are usually relatively small in size and installed close to the point where the water enters the premises in order to treat the whole of the water supply. They are either plumbed into the pipework so that the water flows through them or they are wrapped around the pipework. They are generally simple to install but some require electricity.
The basic principle with electronic and magnetic conditioners is that they encourage the formation of crystals as the water flows through them. When the water is then heated, the scale tends to form around the crystals rather than on the internal surfaces of the boiler or pipework.