A truck comprising: - a vehicle frame, - a door (22, 24) which is at least partially movably attached to the vehicle frame, - a door locking device comprising a handle element movably mounted on the door (22, 24) and having a locking portion including a tongue and a locking pawl for locking the door (22, 24), and - a frame element of the vehicle frame having a mounting section having a tongue opening for receiving the tongue and a latch opening for receiving the latch, characterised by: - an alarm device adapted to detect unauthorised opening of the door locking device, the alarm device comprising: i) a receiving device adapted to receive a signal from an activating device and to arm the alarm device, ii) a sensor adapted to detect whether the tongue is in its locked position when the alarm device is armed, wherein the sensor is arranged on the inside of the frame element and on the side of the tongue opening so that access to the sensor is prevented at least in the locked position of the tongue, iii) an alarm signal output device (116, 152) connected to the sensor and which outputs an alarm signal if the sensor does not detect the locked position of the tongue when the alarm device is armed, and iv) a power supply device connected to the receiving device, the sensor and the alarm output device (116, 152) to supply them with energy. - a vehicle frame, - a door (22, 24) which is at least partially movably attached to the vehicle frame, - a door locking device comprising a handle element movably mounted on the door (22, 24) and having a locking portion including a tongue and a locking pawl for locking the door (22, 24), and - a frame element of the vehicle frame having a mounting section having a tongue opening for receiving the tongue and a latch opening for receiving the latch, - an alarm device adapted to detect unauthorised opening of the door locking device, the alarm device comprising: i) a receiving device adapted to receive a signal from an activating device and to arm the alarm device, ii) a sensor adapted to detect whether the tongue is in its locked position when the alarm device is armed, wherein the sensor is arranged on the inside of the frame element and on the side of the tongue opening so that access to the sensor is prevented at least in the locked position of the tongue, iii) an alarm signal output device (116, 152) connected to the sensor and which outputs an alarm signal if the sensor does not detect the locked position of the tongue when the alarm device is armed, and iv) a power supply device connected to the receiving device, the sensor and the alarm output device (116, 152) to supply them with energy. i) a receiving device adapted to receive a signal from an activating device and to arm the alarm device, ii) a sensor adapted to detect whether the tongue is in its locked position when the alarm device is armed, wherein the sensor is arranged on the inside of the frame element and on the side of the tongue opening so that access to the sensor is prevented at least in the locked position of the tongue, iii) an alarm signal output device (116, 152) connected to the sensor and which outputs an alarm signal if the sensor does not detect the locked position of the tongue when the alarm device is armed, and iv) a power supply device connected to the receiving device, the sensor and the alarm output device (116, 152) to supply them with energy.