An accelerometer for sensing velocity changes particularly suited for passenger restraint systems in a motor vehicle for the deployment of an air bag includes a housing with a magnetic closing element. The magnetic closing element includes a permanent magnet which generates a field around the sensor housing. A restricting element is mounted around the magnet for restricting and concentrating the magnetic field around the sensor. In an alternate embodiment, two similar sensors may be housed in a single enclosure for additional sensitivity. The restrictive elements of the sensors eliminate interference between the sensor magnetic fields.