You can create the same effect as the heating element by using matches or a cigarette lighter to gently warm your key. Don’t make it hot, just warm to the touch – and make sure the naked flame doesn’t go anywhere near the remote control buttons, as this could damage the computer chip.
If you have a straw, you can also place this over the lock and blow warm air into the lock cylinder.
If you’re close enough to your house to be able to trail an extension lead, try using a hairdryer to open your frozen car door lock. A hairdryer is also useful if the door seal has frozen.
Another way to get around a frozen seal is to push as hard as you can against the door. The pressure should break any ice and so allow you to open the door.
Whatever you do, do not pour boiling water into the lock. Not only could this damage any plastic components but most modern cars have electronics within their lock cylinders.