Device for detecting and counting shots fired by an automatic or semi-automatic fire arm with a barrel and moving parts to recock the fire arm, sliding in the axial direction (Y-Y') of the barrel between a front position and a rear position, whereby the fire arm undergoes accelerations in the axial direction (Y-Y') of the barrel for every fired shot, caused by a succession of shocks due to the shot being fired and to the movements of the moving parts, whereby the progression in time of the accelerations is typical for a fire arm and for the type of ammunition used, thus forming a typical signature for the fire arm and for the type of ammunition, characterized in that it comprises an accelerometer (2) with a pass band which is sensitive to shocks in the axial direction (Y-Y') of the barrel and a microprocessor (3) for analyzing the signal (S) of the accelerometer (2) while firing, whereby the microprocessor (3) is equipped with an algorithm to count the number of shots fired, based on the discernment and recording of a shot being fired on the basis of the detection, in the signal of the accelerometer, of all or part of the characteristic elements of the acceleration signature which is typical of the type of fire arm and of the different types of ammunition used, whereby these characteristic elements are recorded beforehand in a memory (4) of the device.