Abstract: An air bag system has an array of detectors positioned under the seat material of a vehicle seat upon which a person or mass can be positioned. The array has a plurality of sensor leaves extending from a plurality of sensor branches. The branches extend from a trunk. Each sensor is of the type which predictably changes resistance upon the mechanical deflection thereof. A deflector is positioned to concentrate the deflection forces on the sensor leaf. Each sensor leaf has a substrate with conductive material on one side and a backer on the other. The sensor array output is supplied to a terminal and then to operation means which are connected to arm or disarm an air bag actuator to regulate the operation of the air bag in accordance with the mass such as an occupant or a child car seat on the vehicle seat.