They, and the front desk, talk to a central server. The lock says, "hey server, I'm lock XXXX and I've just been tagged with card YYYY. The server looks in its database, and if the combination is allowed, it tells the lock to unlock. The front desk makes changes to the database as needed.

They are communicating all the time and when changes happen. When the card is canceled at the front desk, the "cancel" notice is set from the server out to all doors. When an unknown card is swiped in a door, the door requests the key status from the server.

Because when you scan the card, the reader “asks” a server for verification. It’s usually quick because it’s just the door ID and card ID, and the response either “yes” or “not yes”. (A non answer is the same as a no, that’s why sometimes you have to do it twice.)

Why do you say they're probably not talking to the front desk all the time?

If they're not then yeah it'd be a massive mystery, so likelihood is, they are.

Turns out, they are. They're either hard-wired, or they're just powered and communicate with the base station wirelessly.

For the most part the other comments are correct, however in most of these systems the lock has the ability to store the valid keycards and their expected expiry date. This is in case the server or the network go down, the lock will still work.

When a change is made, like a card is lost and replaced, the 'server' will send the lock the new information. So in a way OP is correct in that the locks aren't constantly talking to 'the front desk.'

BTW many office buildings, warehouses etc use the same systems. They just have much longer expiry dates for pemanent employees.

The new card is programmed by the front desk to tell the lock that the previous card should be disabled. The old card isn’t invalidated until the new one is used.

Most locking systems in hotel rooms such as KABA are Ving don't communicate with the front desk unit.

The actual door locks themselves have their address programed into them as well as the current time.

When the receptionist cuts a new key as soon as it's used in the lock it invalidates the previous key unless it's a master key used by staff or an emergency key used by security; they're permanently valid unless the cards are accidently wiped or there's a security breach such as a master key stolen (in which case a new set of master keys is issued).

The new key has its expiry date programmed into it. Once the clock in the lock exceeds the time programmed into the key card then the lock won't work anymore.

They don't need to talk to the front desk all the time. The front desk sends out a message anytime there's a change in the status of any particular key. If a new key is issued the server tells the lock the new key code. If a customer loses their key, the server deactivates that old key and issues a new code to the lock.

>But they're probably not pinging and talking to the front desk every minute of the day

They actually are. Kinda.

There is a central server. Every time a card is swiped the lock asks the central server if the card is allowed to open that lock. The front desk can revoke (and provide) access from each card to each lock individually.

This is the best answer, thanks.

I was thinking of not so long ago when we didn't have constantly connected bluetooth/wifi networks in hotels and there had to be some mechanism for codes to be issued without the lock having constant connectivity.

Thanks, when the system is fitted the locks in the hotel are mapped onto the front desk unit. You can issue keys for various levels with the lowest level being the guest's keycard which is only valid for their room and then individual floor access for housekeepers, then master keys for management and maintenance right up to the emergency key which is used by security which does everywhere in the hotel even secure areas like finance offices and bar cellars. The emergency keys open the rooms even if they're locked from the inside (in case the guest has collapsed).

If you lose or wipe your room key the receptionist will issue either a duplicate key or a "one shot key" (clue is in the name) but when a new guest checks in they get issued a new key. The front desk unit has a set of "rolling access codes" which match the memory in the lock so when the new arrival swipes their key the memory on the lock moves on to the next code making the old code invalid. Once this has been done 999 times it starts from the beginning again.