This probe pen is ideal for checking circuits, fuses, switches and wiring in cars, trailers, boats, motorcycles and other low voltage systems. Connect the alligator clamp to ground, then take the probe to test the circuit. If the indicator light is on, there is electricity. OUR GUARANTEE We are confident that we offer some of the best products on the market. Therefore, we provide a 30-day guarantee. We will make every effort to ensure that you are completely satisfied with your purchase. Online shopping can seem daunting. We want you to know that there is absolutely zero risk of purchasing something. We won't make it difficult if you don't love it. We offer email and ticket support 24 hours a day, 7 days a week. If you require assistance, please contact us. Please contact customer service if you have any problems with your purchase.