Doors and locks for protecting personal safety and properties have been around for many centuries.  The needs for them have therefore been established as essential.  Door lock technology keeps evolving.  Though most locks stay on a mechanical mechanism as of today (insert a metal key into the lock hole and turn the key by hand to unlock), modern locks have become a lot harder to hack or break than previously.  Furthermore, instead of a metal key, some modern locks rely on a 4 digit PIN code in lieu of a metal key.  This is an improvement.  Some modern locks can even be unlocked remotely over the Internet if needed.  So far so good as far as door locks for households are concerned.

What about a hotel with 300 rooms?  Hotels have long changed to credit cards in lieu of metal keys for several years skipping 4-digit PIN.  Those plastic access cards are much harder to hack or break than 4-digit PIN.  Hotel management across the world can no longer operate the hotel without such a system using plastic access cards to unlock a guest room.  These cards are in fact a simple plastic board imprinted of a circuit that contains a many digit PIN (many more than 4 digits).  Both cards and door locks can be set or reset from the hotel reception desk in a fraction of a second.