Monitoring echolocation using SAMs—static acoustic monitors—such as T-PODs or, more recently, C-PODs—has provided a wealth of information on the fine-scale distribution and activity of dolphins, porpoises and other toothed whales. Effects of marine construction noise on these animals have been identified at much longer ranges than expected. Strong diel, tidal and seasonal patterning of the animals’ habitat use has been found including coastal sites that are regularly used only at night. Arrays of SAMs are now being used for longer term monitoring to assess smaller population trends of lower density populations than could previously be assessed within the limits of economic feasibility. PODs have given insights into the significance of seabed ultrasonic noise from sediment in suspension and diel patterns of activity of benthic organisms, and have also revealed unknown sources of very fast trains of tonal clicks.