An explosive substance that will explode if something touches it. Highly useful as a booby trap. An example of a contact explosive is nitrogen tri-iodide, which can be made in a high school chem lab. MacGuyver once tried to make some, but it didn't work. That's the problem with nitrogen tri-iodide, is that you have to get it just right or it won't work. When it does work, it makes a bunch of purple smoke.