There was a spring lock on the door.

门上有一把弹簧锁。

Mrs. Saunders, the caretaker, was about to leave, but she had no hesitation in admitting us, for the door shut with a spring lock, and Holmes promised to see that all was safe before we left.

看门人桑德斯夫人正要离开， 但她毫不犹豫地接纳了我们， 因为门是用弹簧锁关上的， 福尔摩斯答应在我们离开之前确保一切安全。