A time-delay combination lock is most commonly a digital electronic combination lock equipped with a delay timer that delays the unlocking of the lock by a user definable delay period, usually less than one hour. Unlike the time lock, which unlocks at a preset time (as in the case of a bank vault), time-delay locks operate each time the safe is unlocked, but the operator must wait for the set delay period to elapse before the lock can be opened.
Time-delay combination locks are frequently incorporated into money safes as an armed robbery deterrent, since most robbers are unwilling to wait around for the timer to unlock the safe. In many instances, time-delay combination locks are also equipped with a duress code which may be entered to activate the time delay whilst sending a silent alarm to a monitoring centre.
Modern Time Delay Combination Locks can have many functions such as multiple different codes, pre-set Time lock settings (open and close times), pre-set vacation times (Christmas day etc.), Dual code facility and a full audit trail providing a detailed record of the lock history showing who opened the lock, when and how long it was open. They also use a non-volatile memory so that no information is lost if the batteries go flat but will be openable when the batteries are changed after the pre- set time if the correct code is entered.Some electronic combination locks with a time-delay feature require the code to be entered twice. Once to start the timer, and again after the delay period has expired, in order to actually unlock & open the safe.