Easy-To-Use Voltage Detectors -- The VoltAlert ac voltage testers from Fluke are easy to use-just touch the tip to a terminal strip, outlet, or cord. When the tip glows red, you know there"s voltage in the line. Electricians, maintenance, service, safety personnel, and homeowners can quickly test for energized circuits and defective grounds on the factory floor, in the shop, or at home. --- The Volt Alert 1AC is for detecting line voltage from 90 to 1000 VAC.