An acceleration sensor assembly for a restraint retractor of a seat restraint system in a vehicle includes an acceleration sprocket operatively connected to the restraint retractor. The acceleration sensor assembly also includes an acceleration pawl cooperating with the acceleration sprocket to operatively cause lock up of the restraint retractor. The acceleration sensor assembly includes a mass member cooperating with the acceleration pawl to move the acceleration pawl when an acceleration force is present. The acceleration sensor assembly further includes an electromagnet assembly cooperating with the mass member to hold the mass member in a predetermined position until the acceleration force exceeds a predetermined value and the mass member moves to actuate the acceleration pawl to engage the acceleration sprocket to operatively cause lock up the restraint retractor and prevent unwinding of a belt from the restraint retractor.