。
I remember locking the door, you know.
Literal
I [topic-は] door [to-に] key [object-を] locked memory [subject-が] exists [emphasis-よ].
鍵をかける is the idiomatic way to say 'to lock' — literally 'to apply a key.' The construction [past verb]+覚えがある means 'to have a memory of [doing],' i.e. 'to remember having done' — a very natural alternative to 覚えている. The final よ marks the statement as new information for the listener.