Ladies, do you walk around with a tennis ball inside your purse? No? Well, you might want to start (video below).
If you lock yourself out of your car, then all you need is a tennis ball with a hole in it to get back inside, according to NX2 News.
Simply burn a hole in a tennis ball using a key or screwdriver that has been heated up over a flame cooker. Keep the tennis ball with you in your purse, and if you happen to lock yourself out of your car, then you can use it to get back inside!
Simply hold the ball with the hole over the lock, and press down as hard as you can. The air pressure created by pressing the ball forces the mechanism inside the door, thereby unlocking your car.
It's worth noting that this trick only works for cars with electronic locking systems.
More than 16 million people have watched the video explaining how to use a tennis ball to unlock your car.
Predictably, there have been a range of reactions to a Facebook post sharing this information.
One user wrote: "Great idea but now the bad people also know. Doesn't make me happy."
Another added: "Why carry a tennis ball in your purse? It's a lot easier to carry a spare key, less bulky and lighter and more effective than a tennis ball."
Regardless of whether you think it's irresponsible to post such a thing on Facebook, you have to admit, the science is pretty cool, right?