These are swegways, otherwise known as hoverboards or self-balancing scooters.
They've already made a splash in America and you may have seen kids whizzing around on them in the UK. Just look at this guy.
But the fun may be coming to an end: Metropolitan police yesterday warned that they are ILLEGAL to use in public.
The police referred people to updated guidance from the Crown Prosecution Service which makes clear that swegways are "not legal for road use".
The CPS pointed out that because of some 19th-century legislation, you can't ride a swegway on the road or on the pavement.
And if you do you might be liable to pay a £500 fine.
The only place it's safe to ride them "is private property and with the landowner's permission."
There is separate legislation governing electric bicycles, but swegways don't count because "they cannot be pedalled".
The CPS also points out, in its guidance for the larger Segway vehicles, that self-balancing scooter users could be committing a separate crime of driving a vehicle without insurance.