Every year I put up my artificial pre-lit tree at least one light simply will not light up. It is super frustrating and usually I give up and buy a whole new tree. So thrilled to try out the new “Light Keeper Pro” which swiftly and easily fixes light sets. Now I am not very handy so I was at first skeptical but it really was easy to use! Basically its very common for “internal light failure” to be the culprit of the light not working. Simply remove the bulb from the socket, plug the empty bulb socket into the “Light Keeper Pro” and pull the trigger. Electricity runs through the light set and usually fixes the problem. It took me 1-2-3 to have once again running lights. If that doesn’t solve the problem however, there is another option using “Light Keeper Pro”. By pressing the black button and scanning the light set entirely, the built-in “audible voltage detector” will beep until it finds the interruption. Once repaired, the electricity will flow and the lights will glow. Please visit http://lightkeeperpro.com/home/ for more information on this fantastic product! You can purchase “Light Keeper Pro” at Target, Walmart, Ace Hardware, Amazon http://www.amazon.com/Keeper-01201-Complete-Fixing-Miniature/dp/B000R8KBOK/ref=sr_1_1?ie=UTF8&qid=1448844585&sr=8-1&keywords=LIGHT+KEEPER+PRO and many more!