A discovery technique employs a single-conductor-pair identity circuit for a remotely powered device. A communications system includes a first communications device (e.g. and IP telephony switch) capable of supplying power at an interface, and a second communications device coupled to the interface via a multiple-conductor-pair cable. The second communications device may be a terminal device such as an IP telephone or an intermediate device such as a re-wiring device or a mid-span power supply. The first communications device includes a single-pair identity signal generator that generates a single-pair identity signal on one conductor pair of the cable, and a single-pair sensor operative to sense a conduction characteristic of the conductor pair indicative of the presence of a single-pair identity circuit. The second communications device includes the single-pair identity circuit coupled to the conductor pair and activated by the single-pair identity signal to create the predetermined conduction characteristic. Examples of single-pair identity circuits include circuits employing zener diodes and other physical-layer circuit elements.