If you are stuck , a teapot kettle of hot water will thaw and open a car door.
Also keep a bottle of blue washer solvent handy on porch , this you car pour on a frozen door seal and get right into car.
The next step is to make sure moisture is out of lock tumblers with some wd40 first , then follow up with silicone spray. Make sure rubber door seals are dry them spray then down with silicone and wipe with a clothe , do all seals in car and also spray the side window wipers, this prevents windows from freezing shut and makes power windows function improves= less friction.
Last resort , dump a big hot coffee on the lock and it will get you in.