Growing up in busy city centres, you would've heard of the 'sound test' used as a way to disperse groups to prevent anti-social behaviour.
Supposedly, these devices emitted a high-pitched noise which would constantly ring, but the pitch only allowed it to be heard by those under a certain age.
Now though, we've seen a modern version thanks to a hit record producer - which you can try in the video above.
Jarred Jermaine has almost three million followers on TikTok, with the American regularly uploading to his feed to keep them entertained with mashups, throwbacks and others.
Earlier this week, he gave people a surprise with the sound test!
The clip has already been viewed nearly 10 million times, making it one of Jarred's most successful videos so far.
And those who have tested it out have been left stunned in the comments.
One person read: "All of you worried about getting in the 30s? I got 62 - and I'm 18!"
Another wrote: "Did anyone else start to feel it in their throat towards the end?"
While a third laughed "I'm 23 years old - but I can stop hearing it at 10. Which is strange, because I can usually hear the spiders when they start making their web!"
It all comes down to frequencies.
The generally established audio frequency range is 20 Hz to 20,000 Hz - though some can hear less, some can hear more.
As you get older, the range tends to contract on both ends, which leads to the likes of hearing aids being required.
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