When do you know the transmission fluid is low?

Transmission is sealedI learned from a mechanic that my 1997 Isuzu Rodeo's transmission was sealed and that no fluid could be added to it by me. I suspect, from this information, that a person could not determine if the Transmission Fluid is low without unsealing the transmission. DipstickSome automatic transmissions have a dipstick, usually required to be checked when the car is warm. Usually towards the back of the engine compartment. "Feel it"You may also be able to "feel it". If the car takes time to change from neutral/park to drive, or excessive revving is required to get the vehicle moving, this may indicate low transmission fluid.