、。
The lock itself is just a normal cylinder lock, so closing the door doesn't auto-lock it.
Literal
Lock itself [topic-は] normal cylinder-lock is [because-ですから], door [object-を] close-[if/when-たら] auto-lock do [nominalizing-ということ] [topic-は] is-not.
A practical clarification about a door lock. 錠そのもの uses the reflexive pronoun そのもの ('the thing itself,' 'X itself') to emphasize the lock as an object in contrast to other aspects of the door. そのもの is productive: 人生そのもの ('life itself'), 存在そのもの ('existence itself'). ~ということはない is a set phrase meaning 'it's not the case that X,' 'X does not happen' — a softened negation that comments on a general rule or misconception. Here it corrects the user's assumption that closing the door would engage an auto-lock. オートロック (auto-lock) is the loanword, and the する makes it a verb.