A method of identifying a plurality of devices connected in parallel between the wires of a two wire common communications link, wherein each device bears a unique identification number belonging to a defined range of such numbers, wherein a control station scans the devices by sending a succession of interrogation signals along the communications link, the interrogation signals comprising a representation of the identification numbers of the devices, wherein a first scan is carried out with interrogation signals identifying a first set of bits constituted by the least significant bits of the identification numbers, wherein each device is programmed to generate, and to send to the control station, a response signal that includes a checksum, if the representation of the identification number matches with at least a part of the unique identification number of the device, wherein, in the event that two or more of the devices generate a response signal, the response signals will be deemed to be invalid by the control station, and the first scan is paused, wherein upon pausing of the first scan, the control station initiates a second scan comprising interrogation signals identifying a second set of bits constituted by the first set of bits and a further set of bits constituted by the next least significant bits of the identification numbers, wherein successive scans are carried out by the control station, each successive scan adding yet a further set of bits constituted by the next least significant bits of the identification numbers, wherein upon completion of a scan that does not give rise to invalid responses, the previously-paused scan is resumed continuing on from the point at which it was paused, wherein successive scans are carried out until no invalid responses are generated in each level, and wherein, subsequent to identification of each of the devices by its unique identification number, the control station accords a simplified unique address number to each device for use in subsequent communication therewith. wherein a control station scans the devices by sending a succession of interrogation signals along the communications link, the interrogation signals comprising a representation of the identification numbers of the devices, wherein a first scan is carried out with interrogation signals identifying a first set of bits constituted by the least significant bits of the identification numbers, wherein each device is programmed to generate, and to send to the control station, a response signal that includes a checksum, if the representation of the identification number matches with at least a part of the unique identification number of the device, wherein, in the event that two or more of the devices generate a response signal, the response signals will be deemed to be invalid by the control station, and the first scan is paused, wherein upon pausing of the first scan, the control station initiates a second scan comprising interrogation signals identifying a second set of bits constituted by the first set of bits and a further set of bits constituted by the next least significant bits of the identification numbers, wherein successive scans are carried out by the control station, each successive scan adding yet a further set of bits constituted by the next least significant bits of the identification numbers, wherein upon completion of a scan that does not give rise to invalid responses, the previously-paused scan is resumed continuing on from the point at which it was paused, wherein successive scans are carried out until no invalid responses are generated in each level, and wherein, subsequent to identification of each of the devices by its unique identification number, the control station accords a simplified unique address number to each device for use in subsequent communication therewith.