Nothing is more frustrating than walking back to your car only to realise the keys are in the ignition and the door is locked. Depending on your situation, you may have several options to help you unlock the car from the outside. Regardless, it is possible to open the car door, it just may take more time if you are without the necessary tools.
Press the "Unlock" button on the keyless remote. Although the initial keyless remote is probably attached to your keys (which are in the ignition), you typically receive a second and even third set when purchasing the vehicle. This allows you to unlock the car, even with the keys in the vehicle.
Contact AAA, if you are a member. AAA offers free service for unlocking car doors, and with many local agencies that provide AAA service it shouldn't take more than a few minutes for a member to stop by and unlock your car door.
Call a towing services. These service providers also offer the ability to unlock your car door. Although you are charged for the service, you may not have any other option.