Plastic casing with a large display which also serves as a touch screen. A hinged battery compartment cover facilitates the straightforward exchange of the two 1.5 V alkaline batteries type AA. The base can be removed and fitted to all commercially available recessed conduit boxes or directly on the wall, to be wired before the control- ler is fitted. The casing accommodates the electronics with a '& switch and a relay with a potential-free N.O. contact. The connection terminals are integrated in the base.