a sir system has frontal air bags and side air bags both controlled by the same microprocessor . to guard against spurious deployment of side air bags with minimal software burden , a lateral accelerometer and an arming circuit detect side crash activity and apply an arming signal to a pulse accumulator circuit in the microprocessor which monitors the accumulator state to detect arming , thereby inhibiting deployment when the arming signal is absent . the arming circuit receives the accelerometer signal , removes the dc component which is subject to drift , adds a fixed offset voltage and compares the resultant signal to threshold values to produce an arming signal when a threshold is breached .