More commonly referred to as GFCI, a ground-fault circuit interrupter, but you commonly hear people just use GFI. You’ve probably noticed them before (think of the little red “reset” and “test” buttons) because these devices are required by code in wet areas: kitchens, wet bars, bathrooms, laundry rooms, garages, unfinished basements, swimming pools and hot tubs, and any outdoor location. They prevent shocks from occurring to whoever is using the receptacle. Even on a wiring system that is grounded, electricity can leak from the hot lead without tripping the circuit breaker. It works by constantly comparing the amount of electrical current flowing out of and then back into the neutral, grounded conductor. If there is but the slightest difference, the circuitry inside the device shuts itself down instantaneously (in as little as 1/40 of a second). This action prevents you from being electrocuted, which could happen while you were particularly well grounded (for example: turning off a faucet while turning on a defective appliance). GFCI breakers exist as well, and they are used when several receptacles and outlets must be protected at once.