The invention refers to a device and a method for monitoring a delimited area in order to detect if an undesired object is present within the area. The invention also refers to a use of the device. A first laser is adapted to emit a laser pulse (B) of a determined wavelength over the area. A first photo sensor is arranged to receive a reflected part of the laser pulse (B). An evaluation unit is connected to the laser and the photo sensor. The evaluation unit is arranged to measure the reflected part of the laser pulse (B) during a predetermined time period after the laser pulse has been emitted from the laser, to generate a signal depending on the measured reflected part and to process the generated signal in order to determine if an undesired object is present within the area.