Answer: relock

AnswerCrossword Clue
RELOCK

A door may do it automatically when it closes

RELOCK

Bolt down again

RELOCK

Auxiliary vault antiburglary device

RELOCK
Secure anew
RELOCK
Bolt again
RELOCKSecure again
RELOCKSecure the vault again
RELOCKDouble check the door, in a way
RELOCKEnsure security, in a way