Carrying a note to help you remember your PIN, password or lock combination can be risky, especially if thieves get a hold of it. This DIY fake business card will only reveal your secret note when you give it a little heat. In this video from the Shake the Future YouTube channel, you'll learn how to hide any message on a fake business card (like an easy-to-forget PIN) with some thermochromatic pigment and some nail polish. Create and print out a fake business card on some thick paper using a word processor or free template online (a quick Google search will do the trick). Then create and print out an extra logo that matches the card (with your note printed inside). Mix your thermochromatic pigment with some gel effect nail polish, and paint it over the extra logo and note. Then cut out the newly painted logo and attach it to your business card with some glue.
If you press your thumb on the new logo, you'll see the pigment fade and your hidden message will appear. Now whenever you forget your PIN, lock combination, password or whatever you have trouble remembering, you know where to look. And if your wallet or purse gets stolen, thieves will never be able to find it.
The Secret PIN Number [YouTube]