Silly question

[Fearlessagent]

Just make sure you place the callback in the .hps file associated with the map where the door you want to unlock is. If you are not sure how to unlock doors in the first place, check this page and look for the AddUseItemCallback function to be placed in the OnStart() portion of your code. Then just write a function which will unlock the door, remove the key from inventory, and play an unlock sound if you choose when it is called.