Abstract: A wearable device is described that is configured to alert a subject prior to encountering an obstacle. The subject may be visually-impaired. The device includes: a mobile transceiver tag adapted to be worn by a subject within a designated area (e.g., a swimming pool); three or more stationary transceiver beacons in spaced apart, fixed positions; a wearable signal output device (e.g., headset); and a processor with software that can calculate the subject's position relative to one or more obstacles (e.g., end of swimming lane) and sends a left, right, or reverse signal to the signal output device.