Currently, there are no blood pressure monitors providing a proper accuracy of blood pressure evaluation. The novelty of the proposed tonometer is the world’s first use of a compression cuff where the air is replaced by a liquid. This allows realizing the technology of systolic and diastolic pressure evaluation by analogy with the Korotkoff method, without using algorithmic methods. The hydrocuff technology makes it possible to substantially increase the amplitude of oscillations, thus recording moments of appearance and disappearance of Korotkoff sounds by a direct method. This resulted in creation of automatic, autonomous, non-invasive blood pressure monitors with a pressure error of 1-3%.