A system to detect obstacles includes a power beam transmission circuit, a power beam reception circuit arranged to receive a power beam from the power beam transmission circuit, an emitter module, and a detector module arranged to distinguish between a first characteristic and a second characteristic. The emitter module includes a first emitter arranged to emit a first signal having the first characteristic, the first signal emitted in proximity to the power beam, and a second emitter arranged to emit a second signal having the second characteristic, the second characteristic different from the first characteristic, the second signal emitted in proximity to the first signal. The detector module includes a first detector arranged to respond to the first signal emitted by the first emitter, wherein the detector module is arranged to determine when an obstacle is in or near a line-of-sight transmission path between the first emitter and the first detector.