Abstract: A pile driving hammer monitoring apparatus is disclosed to include a pressure wave sensor, such as a hydrophone, remotely located from the pile driving equipment for detecting pressure waves generated by the hammer striking a pile. The sensor generates a proportional analog electrical signal which is conditioned into a corresponding digital electrical signal and conveyed to a microcomputer. The microcomputer calculates the hammer blow rate over a predetermined time period or over a selectable time period or distance of pile movement. Data independent of the blow rate information is enterable into the microcomputer by means of presettable multi-position switches. The apparatus can be powered either by an alternating current source or a direct current source.