This little gadget, called the Zap-It ($(removed) on Amazon), delivers a small electrical shock to a mosquito bite, making the itch stop. It uses a piezoelectric crystal to create the spark, so no batteries are needed. According to the UK's National Physical Laboratory, the shock (which in my experience is less painful than a static electricity zap) "acts on the skin of an insect bite victim to reduce excess production of histamine, and the associated redness and itching. Results from a clinical trial conducted at the London School of Hygiene and Tropical Medicine concluded that more than 90% of test subjects were itch-free within five minutes of using the Zap-It! product."
My family has been using a similar piezoelectric zapper for years to make mosquito bites stop itching. My daughters have also learned that you can zap your wrist to make your fingers twitch, so the gadget doubles as a toy.
They manufacturer recommends starting with five clicks on a mosquito bite, but we zap ourselves 20 times or more. As J.R. "Bob" Dobbs says, "'Too much' is always better than not enough."