This is the 7584th most frequent Russian word.
дымовой
The Russian word "дымовой" means "smoky" or "relating to smoke."
In this sentence, 'дымовой' functions as an adjective modifying the noun 'сигнал', describing the signal as being related to smoke.
Дымовой сигнал был виден издалека.
The smoke signal was visible from afar.
Here, 'дымовую' is the feminine singular form of 'дымовой', describing the pipe as associated with smoke or its emission.
Они установили новую дымовую трубу.
They installed a new smoke pipe.
In this instance, 'дымовыми' is the instrumental plural form of 'дымовой', referring to detectors related to the presence of smoke.