Abstract: A compact and lightweight condition responsive sensor unit of printed circuit board construction includes a deflectable sensor plate integral within a multi-layered printed circuit board and suspended within a cavity formed between a pair of printed circuit boards. Flexure arms allow for movement of the deflectable sensor plate within the cavity in a direction generally perpendicular to the printed circuit boards. The deflectable sensor plate is formed of a conductive material and moves in response to acceleration, inclination, changes in pressure, and other conditions. The conductive, deflectable sensor plate may form the central plate of a differential capacitor, or other sensing means such as contact plates or proximity sensors may be used.