Happily, the same things you can use to prevent frozen car doors and locks can also be recruited to solve the problem.
Most automotive supply shops and departments carry lock deicers of one kind or another. Better yet, most homes have a can of WD-40 lying around somewhere. It works even better and it’s right there.
Why WD-40? The scientists who developed it will tell you their assignment was to develop a lubricant for NASA that would deal with moisture accumulation on space vehicles: W=water, D=displacement, and what we buy in stores was the successful, and 40th, formulation.
First the door locks. Most vehicles have door locks with a tiny spring-loaded cover built into the inside of locks. Its purpose is to keep moisture out. They don’t always work as well as intended.
When they don’t, take the little red tube that comes with WD-40 spray cans and attach it to the nozzle. Next, insert the red tube into the door lock and spray WD-40 into the lock. Be generous.
The WD-40 will not only thaw the lock, it will also lubricate it.
Now the doors. Start with the driver’s door. Once in, you can start the car, warm it up and let the heat thaw the other doors. But you still have to get in.
For now, you have the choice of using WD-40, or hooking up extension cords to plug in a hair dryer or heat gun. If you choose the latter, be careful not to blister the paint.
The better choice is to attach the tiny red tube to the nozzle of the WD-40 spray can and insert the tube between the edge of the door and the body of the car. Spray all the way around the door frame as far as possible. Be generous. Let it stand for five or 10 minutes. The WD-40 will melt the ice that is causing the rubber seal on the door to stick to the door frame.
For door locks, spray WD-40 or any other deicer into the lock before taking the vehicle through a car wash. For extra protection, spray inside the door locks again after leaving the car wash.
For doors, spray a light coat of WD-40 on the rubber seals all the way around each door. Armoral works as well, and also revitalizes the rubber, even better than WD-40. On SUV’s, don’t forget the rear door.