With Christmas now fast approaching, households will be breaking out the old box of decorations including their trusty lights for the tree.
Some might notice that there's a single red light on each string which appears to be a spare, but it turns out the object actually activates a little-known setting.
The finding was shared by a woman who posts under the TikTok user @VizNelly who revealed what happens when you replace one of the light bulbs with the red spare.
