A location system including a base station (120, 200) and a responder tag (140, 250) that communicate using an acoustic signal to determine the location of the tag in a bounded 3D space (100). The base station transmits a request signal (310) encoded with the identifier of a particular tag. The particular tag responds after a fixed delay (t2−t1) with an acoustic response signal (330). The base station determines the location of the tag based on the received line of sight signal (330) and its reflections (340). The response signal may be encoded with data indicating a status of the tag, or data from associated sensors (270) or actuators (280). The request signal may also be encoded with data for controlling the tag or the associated sensors and actuators. A power management scheme may be carried out by the tag.