Open up a Rusty Door Lock
Nothing is more troublesome than coming home to find that you don’t have entry due to a rusty door lock. WD-40 is a light lubricant that attracts less dirt and loosens the rust accumulated in the lock. WD-40 also has a small skinny red nozzle to make it easier to spray into smaller areas. Spray a shot of WD-40 into the lock through the thin nozzle, and you will witness the crazy results within minutes.
source: grandmathing.com
The best part about using this lubricant is that it helps the key fit in the lock, regardless of the amount of rust in it. We recommend investing in a new lock if this is coming up as a consistent problem, but for that, every once and a while issue, WD-40 comes to your rescue.