This reminds me of how in the '90s my university gave out smartcard student IDs that had a little cash account on them for vending machines and dorm laundry roo

This reminds me of how in the '90s my university gave out smartcard student IDs that had a little cash account on them for vending machines and dorm laundry rooms. They installed readers into the soda machines, and they put a central panel in each laundry room with a reader and a keypad for you to indicate which washing machine you wanted to activate. We found out that the vending machine hardware would query the card before selling you an item, but wouldn't debit your account until dispensing it, in case the vend failed. If you timed it just right and removed your card after it was interrogated but before the item dropped, you'd get it for free. The smartcard project was only a 2-year evaluation and the university decided to move away from it, so the smartcard company came and took away all their hardware. When they did this, they took the panel down out of the laundry rooms, but did not fully clean up the wiring coming out of the back of each washing machine. One of my roomates got curious and discovered shorting the leads of that wiring to a battery would mimic the signal the smartcard panel would use to tell the machine it's been "given" a quarter. Do that 3x and you got a 75 cent wash for free.