To more accurately control insertion of penetrating instruments (e.g., trocars, needles, or the like) into a body cavity, organ, or potential space, an accelerometer is coupled to the penetrating instrument. The accelerometer may by employed to measure or detect the sudden lack of resistance which occurs when the penetrating instrument penetrates to a predetermined depth (e.g., through the abdominal cavity, vein, or outer bone) in a more accurate and reliable way instead of practitioners' subjective feeling. An acceleration sensor (i.e., accelerometer) coupled to the penetrating instrument (e.g., trocar or the like) may transform the physical variable `resistance change` into an electronic signal that is then processed in an electronic circuit, and finally triggers an audible/visible alarm and/or feeds an actuating mechanism to control movement of the penetrating instrument.