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.
As reported by the Mirror, the TikToker shared the now-viral clip, saying: "I was today years old when I found out what these are for."
The user went on: "Remove regular bulb and replace."
In the clip viewers can see them doing just that, then stepping back and waiting a few seconds before the lights begin to flash on and off.
Adding the red light changes the lights' settings like a remote control would with a more modern set of lights.
The clip left TikTok users stunned and amassed 19.4million views as well as over 6,000 comments from impressed viewers.
One user said: "I thought they were spares."
A second wrote: "Wait what??????? I thought they were replacements!"
"I swear to god this app has taught me more in the last year than I have been alive," added a third.
A different user commented: "Dude all they had to do was write that somewhere on the box. I wasted so many years not knowing about this."
However, some claimed that they knew what the red light's purpose was all along and were surprised that it wasn't more widely known.
One person said: "As someone who grew up in the 90s…I thought everyone knew this - We didn't always have remote control lights!!"
A second agreed: "I used to put up the Christmas lights at my parent's house, so I didn't know that this wasn't common knowledge."
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