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. 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 (e.g. Christmas Day), 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. This will allow the safe to be opened 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 a second to unlock and open the safe entered after the delay period has expired.