I am trying to make a reaction test circuit where a LED comes on at after a random amount of time and the slowest player gets and electric shock. The switches they press turn on a relay to another circuit connected to the device which shocks them. I need to find a way to stop the slowest players switch working so the fastest player doesn’t get shocked. I also need to know what current and voltage the electric shock should be. Some one told me that it ises a small current and a large voltage. The ones you can but in shops are mostly use 9V cells, but using a op amp would make it 13V-14V which probaly wouldn't be high enough. If anyone has any suggestions to either problems it would be very useful.