An essential tool for anyone who ever dabbles in electrical work, Sperry’s outlet tester uses a series of three lights and an easy-to-read chart to make sure you avoid any shocking surprises. At under $6, it’s within about $1.50 of the best price we’ve seen, but when it’s lower, it’s usually as an Add-On Item. Today’s deal, by contrast, is eligible for Prime Shipping all by itself.