If you own a car, you have probably experienced the panic and frustration from locking the keys inside the vehicle. Locking yourself out of the car can not only cause frustration but also embarrassment---especially if you are in a public car park. You can use different methods to open a locked car door, but many methods can break your door lock, or even the window glass. For keyless-entry car locks, you can easily use a tennis ball to unlock to the door.
Find a tennis ball at home, or purchase one at a local sporting-goods store. Cut a small hole about the same size as the keyhole on your car door into the side of the tennis ball; use a small kitchen knife or a nail to puncture a hole. You can also use a lighter to burn a hole.
Press the tennis ball hole against the key hole, squeezing the ball until the air pressure causes the door to unlock.
If the door does not unlock right away, continue applying pressure.
The tennis ball trick may only work for cars with keyless-entry door locks.