This smart reverse warning devise reacts to the environment. Using a built-in microphone, this warning devise constantly measure the ambient noise level. A built-in microprocessor automatically adjusts the volume of the warning tone so that it is only about 5 dB above the measured level. In this way it is guaranteed that the warning sound is always loud enough to be heard by all persons in the danger area. At the same time, this prevents the warning sound from being too disturbing, especially in a quiet environment.