Hall sensors
WARNING: This page is about a different car, the 2001 Saab 9-3. However, it is still accessible from the selected car via links, so may be relevant.
The pulse emitters for the seat are of the Hall sensor type and integral to the motors for the function concerned.
On the motor shaft is a 2-pole magnetic ring (north/south). In the end of the motor is a Hall sensor which detects changes in the magnetic field. When the motor is running, the magnetic changes occur twice per rotation.