Nobody wants to live in a world where just anyone can look in on anyone else’s mail – but sometimes you really, really need to know what’s in that envelope. For sneaky people who have $15 to spend, Envelope X-Ray Spray helps you be sneaky without getting caught. The spray does just what it says: when you spray it onto an envelope, you can see straight through the paper to find out what’s inside.

The spray turns the envelope (or any other paper) temporarily translucent, allowing you to more or less see through it. For thirty seconds, you can snoop to your heart’s content. After that half minute, the envelope goes back to normal with no residual effects, marks, or discoloration. The best part of this particular product is the Amazon review that begs for help after a buyer accidentally sprayed his hand invisible.