A consortium composed of Thelma Biotel and Center of Oceanography developed and tested an acoustic 3-axis accelerometer transmitter. The first testing phase took place in experimental tanks and consisted of externally attaching prototype data logging tags in Lusitanian toadfish (Halobatrachus didactylus Bloch & Schneider, 1801) and comparing raw logged data with observed behaviours to obtain characteristic accelerometer data patterns that could be assigned to those typical movements. Four behavioural “signatures” were considered, two different burrowing movements, attack towards a prey and general activity. The second phase was the development of a prototype with integrated software capable of identifying those accelerometer typical patterns, process the information and transmit relevant data acoustically. Burrowing movements and activity were detected and transmitted with 100% accuracy while attacks were detected with a 61% successful rate. The third phase took place in the Mira estuary (SW Portugal) with 2 groups (five and six individuals each) of free living toadfish to test the codified acoustic signal transfer from the AccelTag to the acoustic receiver array. The novelty of the AccelTag is that is has the measuring capabilities of an accelerometer archival tag but without the necessity of recapture the tagged fish, since it has the ability of analysing the logged data, extract very detailed species dependent information and transmit the relevant processed data.