Abstract: A seat position sensor rail device is disclosed, comprising an upper rail body to partially support a seat, a lower rail body which slidably engages the upper rail body, a position sensor device mounted on the upper rail body, and a contact plate member secured to the lower rail body. The position sensor device comprises a pivotal contact lever device having a magnet member and a magnetic field sensor device. The contact lever device gets in contact with the contact plate member, angularly displacing the magnetic field generated by the magnet member. The angular magnitude of the magnetic field is detected and the data is utilized in controlling deployment of an airbag system.