A voltage tester is a lifesaver--and I mean this literally. Unlike other helpful, time-saving home remodeling-related gadgets that we call lifesavers--paintbrush combs, Zip Walls, or paint sprayers--voltage testers can aid in the prevention of injury or death from accidental electric shock. In fact, I rated voltage testers are one of the five best tools you can buy for home remodeling.
Find an electrical receptacle that you positively know is live. Typically, this is a receptacle that is powering an appliance, radio, TV, computer, etc. Make sure that this appliance is on.