3D20: There is no door lock or monitoring on the Dremel 3D20. 3D40 and 3D45: The doors are monitored, and both doors must be closed to initiate a remote print from the Dremel Printcloud. This ensures that there are no hands inside the printer when a print is started from a user who is not near it. During any other time, including building an object, opening a door will cause a warning notice to display on the screen.