The idea that Australia is always warm and sunny is somewhat of a stereotypical view. While this might be largely true in the northern states, the south of the country certainly gets its fair share of winter. The cold can affect car locks, and if you've had issues unlocking your car when the weather is cold, then your lock might be freezing up. This can feel like a real catastrophe if it happens late at night and you need to urgently use your car. Before you call a 24 hour locksmith, there are a few things you might want to try yourself.
1. A Cup of Hot Water
Boil your electric jug and fill a mug with hot water. Hold the mug directly under the lock so that the steam rises up towards it. Do not hold the mug directly against the door of your car. While it's unlikely that the heat from the mug will damage your car's paint, it's better to not risk it. Try your key again to see if the lock opens without issue.
2. A Hot Key
You will need a pair of pliers and a cigarette lighter. Securely grasp the bow of the key with the pliers. The bow is the circular end of the key that you hold onto. Do not try to use tweezers or an oven glove, as your grip will not be secure enough. Using the pliers will protect your hand against the heat. Activate the cigarette lighter and hold it so that the flame touches the shoulder and tip of the key (the long portion with notches). It will only be necessary to do this for a few seconds, and you should stop immediately if you notice that the key is turning red from the heat. You don't want to damage the key. Try to insert the key into the lock. The heat should evaporate any ice that might be inside. Do not try this if the bow of the key has a plastic coating, as you can easily melt it.
3. A Specialist Product
If a frozen car door lock is a common occurrence in the winter months, then it's best to keep something handy in order to deal with it. Buy a specialist de-icing spray, which can be found at any hardware shop. You simply spray it on your key and insert it into the lock. You might need to jiggle your key in order to disperse the liquid into the lock's mechanism. You can even make your own de-icing spray with isopropyl alcohol (rubbing alcohol) and water.
If none of these methods work, then you should not persist, as you might damage your lock.
There might be an internal fault with your lock as opposed to an ice-based obstruction, and so you should have the lock examined as soon as possible.