CHICAGO (CBS) — Dog owners know it is never a good idea to keep a K-9 in a hot car.

Customers at a Cracker Barrel in Romeoville stopped in for a meal and left their dog inside–with the car running. They included a note that said: “Please don’t break windows … air conditioning is on!!!”

While the owners left the air conditioning on for their pooch, some call the idea less than full-proof.

It is illegal in the state of Illinois to keep your car running in that fashion.

Animal advocates add in the event the car runs out of gas or the dog accidentally sets the car in gear, it could be dangerous for the dogs and others.

In addition, some keyless engines can shut off if the car’s key-fob or key chain is far enough from the vehicle.

Last month, a dog was rescued from a Chicago parking lot. People passing by were able to open the car door through a cracked window with the permission of police officers. The dog was okay.