The invention relates to a device for the active monitoring of the safety perimeter of a motor vehicle, which is used to detect moving objects or static obstacles inside said safety perimeter. The inventive device includes a first sensor which covers a first detection zone comprising at least part of a blind angle of the vehicle and which sends input signals to an information-processing device which generates output signals for means used to alert the driver. Moreover, the device also includes at least one second sensor which covers a second detection zone and which forms one unit with the aforementioned first sensor. According to the invention, the first and second sensors co-operate in order to cover a combined detection zone containing the blind angle, which is increased in relation to the zone covered by the first sensor and which forms a section of the safety perimeter. The above-mentioned unit comprising the first and at least one second sensor use the same alarm means.