A car locksmith uses many tricks to enter a vehicle if the key is locked inside. The methods, however, set the alarm off, but they are effective. Here is a method that a car locksmith can use to open and enter a vehicle without a key;
A metal rod (thin)
A small airbag
A big airbag
Wedge (plastic, vinyl, metal)
The first step is to place the wedge on top of the doors.
That will allow the door to create a gap. The gap should be big enough for easier use.
Next, they place the small airbag in the space (on the side of the door). Then the air is pumped to allow the space to expand more. Once the space is created, the car locksmith removes the wedge since it will be needed to create the gap on the other sides of the door.
After that, the car locksmith places the small bag on top of the door and pumps the air to allow more expansion. Once the gap is big enough, they take the metal rod and try to open the door either by pressing the lock or opening it manually.
Any person can use the above method to open their cars. A precaution, though, if it gets hard, it is advisable to seek help.