The Cash Can is a small brass tube just big enough for a rolled-up bill. The tube can't be opened unless you remove it from your key ring. It's as easy to remove from the keyring as your keys are. It's also unobtrusive -- the whole thing is shorter than most of my keys. Even though I live in a city with an ATM on every block, I'm big on always having a spare $20 bill at hand. I've usually got one stashed in my car and another in my gear bag, and a third tucked into my wallet. The advantages of the Cash Can are its workmanship and stealthiness -- unless they read this review, few people are going to know what's inside the brass tube. It just looks like a key fob. Plus, if I lose my wallet, at least I've got the cash attached to my keys.