Recently, fluorescent proteins have become an indispensable tool for in vivo visualization of various processes occurring in living systems, from individual organelles to whole organisms. They allow observing the expression of proteins, their localization, and are also suitable for monitoring biochemical processes in cells. As a rule, fluorescent proteins have pH-dependent spectral properties, which make it possible to design genetically encoded pH sensors on their basis for solving various biological problems. In this work, we have obtained a set of extracellular pH sensors based on the SypHer3S protein, which has pH sensitivity in the pH range from 7.4 to 9.0. For this purpose, chimeric SypHer3S constructs with various transmembrane domains of membrane receptors were created, allowing the targeting of this protein to the outer side of the cytoplasmic membrane. Their subcellular localization was characterized and the most successful version of a chimeric pH sensor for measuring the extracellular pH value was selected.