The performance requirements for a powerline proximity-warning (plpw) system include high probability of detection at a dependable alarm range, low probability of false alarm, no setup or calibration, and little maintenance or adjustment. These requirements can be met by a system that explicitly measures range to the line. Candidate techniques include microwave radar, optical radar, and sonar. The six specific concepts that appear to be technically feasible in the plpw application are (1) microwave gated- pulse radar, (2) microwave chirp fm-cw (frequency-modulated, continuous-wave) radar, (3) baseband pulse radar, (4) optical chirp fm-cw radar, (5) optical gated-pulse radar, and (6) sonar. The performance of both optical-radar techniques is degraded by dirt and grime on the transmitter and receiver apertures. Proper operation in a construction environment necessitates either daily maintenance or a windshield wiper. The former is expensive and bothersome, while the latter reduces reliability. Baseband radar appears well suited to the plpw application. The cost is expected to be comparable with that of an electric field plpw system. Development and testing of an experimental model are therefore recommended.