I recently purchased a 6" and 9" ventlock. For those of you who have been holding off because it was unclear how the installed product could be safe from removal by unauthorized persons, I discovered that the silver "hook" end is actually threaded, and can be tightened down on the "u" latch within your cars door jam. The solid steel box on the other end is then engaged by the doors locking mechanism, which means it cannot be rotated and unscrewed, resulting in a secure attachment (There is a utube video out there which really explains it well). This system works well on my 2014 E-350 Ford van with church doors in the rear, allowing the door to be securely held open far enough for ventilation while preventing almost all unauthorized access to the dog crates inside. Great system. Just make sure any openings secured with the vent lock, rolled down windows, etc. DO NOT allow any type of access to the remote unlock buttons.