What I do is just keep plenty of methanol (also called "methyl hydrate") on hand along with suitable applicators to get the alcohol into the space where it's needed. Methyl hydrate dissolves ice.

Most often, when a lock freezes, what's happened is that capillary pressure has drawn water into the tiny gaps around the tumblers and around the lock cylinder. When that water freezes, it prevents the tumbers from moving up and down and the cylinder from turning, so even if you can get your key in, you can't rotate the cylinder to unlock the car door.

By having some methanol available in a spray bottle or squeeze bottle designed to fit into a keyway, you can squirt methanol into the lock to dissolve the ice. Once you do that, the lock will work normally.

Methyl hydrate evaporates completely without leaving a residue.

PS: Never use an oil or a grease in a lock. Airborne dirt and dust will stick to the oil and grease, causing that lubricant to gum up the operation of the lock. It's best to use graphite powder in locks because airborne dirt and dust won't stick to graphite. The "dry graphite" aerosol sprays you buy at hardware stores for lubricating locks and light machinery are so named because they use a propellant that evaporates completely, leaving behind only the dry graphite powder.