Abstract: The invention comprises a pressure actuated switch which is actuated when the inlet port of the device is exposed to a preselected pressure. A piston size, and one or more shear pins, is selected for the desired operating pressure, the piston area being inversely proportional to the desired operating pressure. Shear pins are preferably of one size and material. When the desired operating pressure is applied, the force of the piston causes the shear pin to shear thereby allowing an electrical contact to complete an electrical circuit and initiate operation of a selected device such as a recorder, perforating gun, etc. If a single shear pin is used, with any selected piston and desired operating pressure, the shear force applied is a constant; i.e., for any given operating pressure and selected piston size with a single shear pin, the applied shear force is the same. If two shear pins are required, the applied shear force is doubled.