For decades, no, centuries, this invention would’ve made a killing in the free market: a spray that momentarily shows you what’s inside an opaque envelope. As it stands now, the Envelope X-RAY Spray ($14.49) is still pretty cool, but our sources say it does not work on email. Rats. If you can get past that flaw, you’ll enjoy a whole new world of spy-like action. The spray turns any opaque paper translucent for about 30 seconds, then that paper returns to its original state–no markings, no discoloration, no paper trail.