I used to use the Alexa in my roommate's bedroom. By use, I mean that I would yell, "Alexa, add $RANDOM_ITEM to cart/wishlist" through their closed door and it would.

It was a funny prank but I was astonished to see that it wouldn't do any sort of voice detection and if I said "buy items in cart" I'm sure it would have done it without any biometric confirmation that I actually was who I said I was.