Bang Pen This classic practical joke has been around for over 50 years, just place a harmless cap on the device and this ordinary looking pen will deliver a surprise to the next person who takes the cap off. Updated to a modern looking pen so you have them at a surprise if they are expecting the old original type. How it works is a harmless cap that goes off when it is set off, its just enough to startle and have some fun pranking with this practical joke product. Uses any type of harmless strip caps to get the bang effect, these are not included. Have fun with this classic practical joke to prank your family and friends.