The TPI Low AC Locator 40 is a non-contact, pen-style voltage detector that detects 24 to 90VAC and is operated by touching the tip to a connection point or insulated wire. A glowing red tip indicates the presence of live voltage. The detector runs on two AAA batteries (included), is rated Category III, is Underwriters Laboratories (UL) listed, and has European Conformity (CE) marking. Applications include detecting AC voltage in lawn irrigation equipment, thermostat controls, vending machine changers, and other low voltage equipment.

Voltage testers detect electrical current in cables, cords, circuit breakers, switches, wiring, and other components of electrical systems. They can test for live circuits, proper grounding, adequate voltage, and flowing current. They might be used by homeowners to test electrical outlets or by linemen to test power lines. Available in a variety of styles and levels of sophistication, some models simply indicate the presence of electrical current, while others record or display the level of voltage conducted. Some have additional capability such as the ability to perform continuity tests.