A fast-food restaurant with exit treadmills
There is a restaurant in half of the building. The other half is a gym. Customers can walk into the restaurant and eat, but must leave through the gym.
The computer in the treadmill knows what the customer had to eat, and will open the exit doors only when the customer has burned enough calories.
Customers can also enter through the gym, but will not be able to enter the restaurant after using the treadmills. Similarly, the staff will proportion the served food so the calorie calculation checks out.
The manager of the restaurant is considering an in-between room where customers eat while on treadmills. If customers don’t accidentally swallow their food, he can open a new and smaller branch downtown.