Car Locks - Unfreeze Door Lock, how to pick car lock
Squirt de-icer into the lock, using the extension nozzle to push aside the protective inner flap.
Soak a sponge or cloth in hot water and apply it to the outside of the lock.
Heat the key with a flame, this may take several tries, but never force the key as this may result in it breaking off in the lock.
If you have nothing else available to help try placing a warm hand over the lock and keeping it there for a couple of minutes, changing hands every so often.
As prevention is better than cure, to avoid door locks freezing in the first place, they should be lubricated with a graphite based lock lubricant, which will also prevent the locks from wearing.