Abstract: A self-contained tool incorporates an electronic system for significantly reducing the number of batteries required to detonate an explosive downhole, making the tool short enough for transport by helicopter, rather than by boat, to an offshore well. This shortness is further beneficial for negotiating tight-radius bends in deviated wells. Safety is improved by a shear pin holding a pressure-activated switch in an open position until sufficient pressure shears the shear pin. Control from the surface is provided in applications where fluid pressure is controlled at the surface and raised to shear the shear pin. Longer run-in time is better accommodated by the combination of the electronic system and the shear pin.