An add-on device which fits the AEROTEAM IV harness. 
Its simple red and green color code to enable the instructor to validate that the cross check has been completed.
 
Make sure you have carried out the roping safety checks.
The VETO add-on module is attached to the AEROTEAM IV harness. It works on the basis of a red and green color code. This allows instructors and supervisors to validate that the rope knot and belay device have been properly checked before starting any climbing session.