Tom, I believe Robinlo means a system made by / similar to Fike. It does as said, in that it only uses 2 cores and you install "devices" on this cable. The most common device is the detector / sounder. Each device has a range of options that enable it to be a smoke detector, a heat detector, a combination, as well as being a sounder. They are NOT addressable and are favoured by electricians "as they are simple to install and make a great profit" However unlike most fire alarms you can easily remove any device and the panel will not indicate that a device has been removed. There are also available just manual call points and strobes, but I have yet to see one fitted. (I am not saying the MCP are never fitted, just I haven't seen one as they are not cheap)