Hand Buzzer

Classic prank. Shake hands with your victim, it can be quite startling when your victim is not expecting the sudden buzzing sound.  This item is standard equipment for all aspiring pranksters.
 
Just wind the spring-loaded device up and put your middle finger thru the retainer ring to hide it inside of your cupped hand.
 
You can also pretend there is a "Bee" on your victim's backside,  and then touch the buzzer to the back of their shoulder and watch them jump!
 
There is no electric shock and it is completely harmless.