A safety arrangement for detecting the position of an occupant (4) of a seat (1) which is provided with a safety belt (9) which is mounted on a retractor (10) includes a sensor (11) which measures the length of belt withdrawn from the retractor The sensor is associated with a processor unit (8) which is associated with a seat position sensor (7). By determining the position of the seat and by determining the minimum length of belt paid-out from the retractor (10) after the seat belt has been buckled in position, and by determining how additional belt has been paid-out at any incident, the position of the seat occupant (4) relative to an air-bag (19) can be determined. If the seat occupant is very close to the air-bag, the nature of deployment of the air-bag can be moderated by the central processor unit (8).