Good Asian horror movies have a way of taking ordinary items and making them creepy. This is very much unlike American horror movies which relies on the 'shock' factor. Door Lock, which doesn't have any big-name actors, turned out to be quite the though-provoker.
Do you know who has been in your house?
If you live alone and your building either doesn't have security or has lax security, then it's easy for a stranger to break in while you're away, regardless of the type of lock you've used. Now, what if that said stranger decided to hide in your house till you arrive and do things to you while you sleep?
I shan't spoil the movie for you, but i have to say that it has made me want to get a hidden security camera to record anyone coming in and out of the front door. Car cameras have become ubiquitous and i think the same will be true of front/back door cameras.