At my recent stay in Paris, I spotted this note in a Hilton room:

"Dear Guest,
If a product is taken out of the minibar and you decide that you not want the product, please put it back within 20 seconds, otherwise a charge will be raised on your bill.

Our minibar system is equipped with sensors and items will be billed automatically when taken out, therefore please do not use it as a storage space for your own products.

Thank you."

Sensors? What kind of sensors would that be? Weight sensors? Laser beam room detectors?

Anybody out there who knows, how this new (at least to me) minibar technology works?