A sensor (1) comprising a casing (2) delimiting an internal volume (3) and having a passage (31) between the internal volume and a first external zone (Z1) external to the casing; a moving part (4) moveable inside the internal volume (3); detector (5) for detecting a movement of the moving part (4) comprising a detection portion (51) extending in the passage (31) and having a groove (52) open to the outside of the detection portion (51), the groove (52) extending between the first external zone (Z1) external to the casing and the internal volume (3) internal to the casing. The sensor (1) comprises first sealing structure (14) positioned around the detection portion (51) inside the passage (31), the first sealing structure (14) being arranged in such a way as to prevent fluid from passing between the internal volume (3) and the first external zone (Z1) via the groove (52).