Door stops are usually used to hold doors wide open, but did you know that when you travel, you can use them as a low-tech way to keep your hotel room more secure? Close and lock your door, then slip this rubber wedge firmly underneath; it’s virtually undetectable from the other side, and won’t cause damage. The stainless-steel hook handle makes it easy to remove with a quick tug.

$15.47 at Organize.com.