An address system for at least one fire loop 20 includes at least one remote unit 14, 16, 18 and an address card 102. The remote unit 14, 16, 18 is for installation on the fire loop 20 and for addressable communication via the fire loop 20. The address card 102 is for use with the remote unit 14, 16, 18 in order to provide an address for the remote unit 14, 16, 18. The address card 102 includes one or more of a plurality of optically recognisable colour elements 201-210 for encoding an address. The remote unit 14, 16, 18 includes an optical sensor 116 for identifying colour characteristics of the optically recognisable colour elements 201-210, and a control system 118 for determining the address from the colour characteristics.