Beneath the carpet is a mesh of optical fibres that detect and plot movement as pressure bends them, changing the light detected at the carpet's edges.
Hamilton has said the seed for her plot came from the 2005 Tony Award-winning Broadway musical Light in the Piazza, and the original novel by Elizabeth Spencer on which that was based.
It would mean that, in the north of Scotland, it did not get light until 10am in winter, and the Scots have therefore decided that it is a Sassenach plot to ensure that the Highlander is kept in the dark.