Christmas lights are going up on homes and even trees earlier and earlier every year. Before you pull out those old strands of lights you might as well prepare yourself to find some of the lightbulbs won’t work like they did last Christmas.

Incandescent tree light sets are not often well-made and during storage, bulbs can be broken or their wires to come apart inside the socket. If you’re in charge of setting up the tree with lights, you probably know one bad bulb can spoil the entire set.

If you’ve ever plugged in a strand of lights to find only a section actually lit up, the reason is there’s a problem with one bulb. One bad bulb breaks the circuit keeping lights on the other side of the circuit from lighting up.

In the past, you either tried to find the bad bulb by unplugging and then re-plugging the light bulbs but now there’s another way. A tech gadget called The Lightkeeper Pro that my friends were telling me about.

I picked one up at a hardware store for about $22 to test it out. Here’s how it works: The Lightkeeper Pro gadget looks like a plastic gun.

When you plug in the set of lights, remove one of the bulbs that work and place the socket into a slot in the Lightkeeper Pro Pull the trigger to send an electric pulse through the strand at such a rate that it leaps past the bad bulb (wherever that is).

All of the lights should turn on, except the bad bulb. Then replace the bulb you removed and the bad bulb with a good bulb and the strand should light up from one end to the other.

That generally works but if you run into a problem the Lightkeeper Pro has an audible beep to identify where the circuit is broken by clicking the trigger on either side of the bulbs. When there is no beep, you’ve found the bad bulb that breaks the circuit.

The original Lightkeeper Pro works only on incandescent light bulb sets. The company also has the LED Keeper to diagnose and repair LED light sets.