Upon addition of the water, the chemical reaction will begin almost immediately.  Exit the vehicle and shut the door.  At that point you can look inside the vehicle to see bubbling inside the tin reaction container.  This indicates the release of Chlorine Dioxide gas.  Note that the gas may NOT be visible inside the car.  This is normal.  Again, do NOT open car door during the 1 hour treatment time.  Upon completion of the treatment, the liquid inside the container will be orange colored.