The invention relates to a system for monitoring the interior of a vehicle, wherein changes occurring in the occupancy of a seat, e.g. with a person P, a child seat K, an empty seat L, or an occupancy in another occupancy category, are effected in a computer unit by means of transitional probabilities which are externally specified to the monitoring system and which reflect the rapid speed at which a change in occupancy is taken into account by said monitoring system. As a result, an associated airbag or another safety device is activated or de-activated accordingly.