They're called "hoverboards" and they're the hot, tech toy of the holiday season. But some aren't so happy they're flying off shelves.
Doctors say the self-propelling gliders, powered by a lithium battery, are almost certain to send kids to the emergency room.
"We're going to see broken wrists, broken collarbones, concussions, scraped up knees, elbows," says Dr. Rachel Coel, a pediatric sports medicine specialist with the Queen's Medical Center.
"After the Christmas season, by the time spring break hits, and everyone's out there riding, I think we're going to start seeing them a lot more."
Recent reports of some boards catching fire have also raised concern.
Mililani High School student Reyn Aubrey, 17, who sells the gliders online, said the models catching fire didn't have an automatic shut off for the lithium battery and therefore, the battery may have overheated. He says the boards he sells all have the shut off.
Despite safety concerns, the boards are being snapped up online; some cost upwards of $400 to $700.
Doctors suggest parents leave a little room in the budget to add a helmet, wrist guards, knee and elbow pads to go with the glider.
Hoverboards work similar to Segways; users lean forward to go forward and lean back to reverse. Turning just requires a slight shift in weight. To stop, the user just stands up straight. Hoverboards can pick up speed quickly to about 10 miles an hour.
Since the summer, when Aubrey launched his business, sales have picked up significantly.
"When I first started, I was selling two to three a month, which was slow. But recently it's been like two to three a day. So it's really been incredible," he says.
The fully-loaded hoverboards are especially popular. They have colored lights and use Bluetooth to connect to mobile devices.