ABSTRACT: Interpretation of diving profiles of aquatic animals would be considerably enhanced by additional behavioural information. A new sensor is presented here which records animal movements. This sensor was tested on a captive loggerhead turtleCaretta caretta which showed similar activity patterns to free-living green turtles Chelonia mydas. A computer program with user-selectable options was developed to analyse the data consistently and rapidly. Using our sensor wecalculated the total resting time, which differed by less than 5% from the real resting time when the sampling interval was 2 s. The method was additionally tested for different sampling intervals to find out its applicability for field studies.