Location sensing provides endless opportunities for a wide range of applications in GPS-obstructed environments; where, typically, there is a need for a higher degree of accuracy. This work focuses on robust range estimation, an important prerequisite for fine- grained localization. Motivated by the promise of acoustics in delivering high ranging accuracy, it presents the design, implementation and evaluation of acoustic (both ultrasound and audible) ranging systems. It distills the limitations of acoustic ranging; and presents efficient signal designs, detection algorithms, and information...