補ほ助じょ錠じょう

noun

auxiliary lock; supplementary lock

An additional lock installed on a door or window for extra security, often used alongside the main lock.

• 一人ひとり暮ぐらしなので、玄げん関かんに補ほ助じょ錠じょうを付つけました。

  Since I live alone, I installed an auxiliary lock on the front door.