Here is an interesting puzzle that we faced in real life a few days back. We had come back after a beautiful day in Verona and finally we were all ready to retire. Next day we had to leave for Rome early in the morning and that posed a logisitics issue. We had four rooms in our resort – one for our daughters, one for Sunil’s sons and one each for the set of parents. Now the resort we stayed in gave us only one door keycard for every room. Once you entered the room, you had to put in the keycard in a slot next to the door and that triggered the power in the room. Without this, the lights and AC wouldn’t work.

The issue was that while the adults were ready to sleep a little after midnight and wake up early, the kids were notorious for sleeping much later and showing no signs of getting up till 10 am. No amount of knocking on the heavy doors had helped in the past.

The puzzle was how to wake up the kids early next morning. We needed to enter the room. But the keycard was required to be inside – else the power would not work. Thus we could not possibly enter the room.

So, as a first shot, I yanked out the key from the power slot and put in a paper card of the same size. That would not work. I put in a credit card. That would not work either. (If it actually worked, obviosuly, the parents would keep their kids’ room keys with them and use them to enter the kids’ rooms next morning and wake them up). Later I found out from the resort folks that indeed only a hotel card would work for the slots. Apparently the hotel cards had a chip inside (not the magnetic strip) – which is what they programmed when they gave us the keycard. The door cared about the room coding. The slot reader however, did not care how the chip was programmed – it just needed to detect a chip in the card at the right place.

We were way too lazy to come out of the building and walk up across the resort to the lobby to pick up extra cards.

BTW, Sunil had a bright idea that let one parent sleep with one kid that night – which would have worked, but the kids immediately voted the idea down. But we did find an elegant solution.

Can you solve it?