If you’re not familiar with the Under-the-Door (UtDT), it’s a device that fits between the physical gap at the bottom of doors, is then rotated upwards, grasps the lever-style door handle, pulls down and opens the door from the inside. It’s very easy to use, and is publicly available for purchase.
Under-the-Door tool being used (Tim Roberts):
Protecting Against This Attack:
The quickest way to protect against this tool is to simply put something in the way to prevent the tool from getting behind the lever handle. This removes the ability for the tool to pull down and engage the lever handle.
So, how do you do this when traveling, if you don’t bring anything fancy with you?
Easy! Put a towel inside the handle!
For more long term solutions, where you have permission to make physical modifications to the door, simply screw something into the door to block the side of the handle.
Many things will work. Here is a sample of what I’m talking about:
Super simple, yet super effective!
There are also much more visually appealing options as well, thankfully!