TSA inadvertently shows the dangers of master baggage keys

[DetlefK]

3. My lab uses a transponder-system:

Each door-lock is an electronic reader.

The key is a transponder with a rechargable battery that lasts ~24h with sparse use, ~36h without use. The whole things is encapsulated in plastic. Every transponder has a unique signal.
(The thing looks like an especially large and thick plastic-coin, with a ring to attach it to a key-ring.)

You have to activate the transponder every day: You hold it to the recharging-station, it reads out the ID and checks at a database whether the transponder is active (or inactive or has been reported as stolen). Once the ID has been confirmed, the device charges the battery wirelessly (~5 seconds).
If a transponder gets stolen/lost, it can only be misused in the time-window as long as the battery is still good. Once it's registered as stolen, you cannot recharge it anymore and it becomes useless.

Each electronic door-lock is programmed only to accept transponders of a certain group. It can be read out, who was the last person to open that lock.