A control or supervision system incorporates a digital serial communication and modules which are mutually communicable to this and operate with CAN-protocol. A control desk can be wirelessly connected to one or more modules operating with a signal protocol which takes no account of arbitration and/or confirmation functions appearing in the CAN-system. A particular receiving communication part executes the conversion of said signal protocol to the signal protocol of the CAN-system. A device for controlling a function in a first module in a CAN-system via a wireless connection to a second module in said system. A system of mutually separate units, whereof each unit operates with a CAN-signalling protocol, intercommunicable by means of radiocommunications operating with an identification system in which a key allocation between the units is based upon identities that are assigned by a module in the unit or a master system.