Access control, in the physical sense, is a system used to permit access to authorized people and deny unauthorized entry. Most commonly used by employers to secure their buildings where employees and visitors use a key card to gain entry. These key cards can be controlled remotely to be activated or deactivated.
Access control systems can be equipped with battery backups for the controllers, readers and door locks to maintain functionality during power outages. If the power outage lasts long enough to drain the batteries, the doors can still be opened from the inside or with manual keys.
If a card is lost, stolen or damaged, you can easily disable the card through the management software. After which the card cannot be used in the system (unless reactivated) and any further attempts to use that card will be recorded.