Sensor device for optically detecting characteristics of a fluid, comprising a housing including a base portion and first and second hollow appendages (4, 5) in the form of fingers extending from the housing along respective longitudinal directions and at least partially facing one another, wherein in use said fluid is present between said first and second appendages (4, 5), first and second optoelectronic devices (13, 14) capable of transmitting and receiving radiation, respectively, mounted in a housing cavity (6, 7, 8; 19) formed in the housing, in the first and second appendages (4, 5) of the housing respectively, said housing cavity (6, 7, 8; 19) being open towards the base portion of the housing; the arrangement being such that in use a radiation beam transmitted by the first optoelectronic device propagates in an optical path which includes a portion crossing the fluid between said appendages (4, 5) and reaches the second optoelectronic device; wherein said optical path comprises a plurality of reflecting surfaces (10a; 11a; 21a; 22a) adapted to deflect the radiation beam between the optoelectronic devices (13; 14) and said fluid crossing portion, said reflecting surfaces (10a; 11a; 21a; 22a) being made integrally with said appendages (4, 5) of the housing; whereby first and second internal cavities (10, 11) are formed in distal portions of the first and second appendages (4, 5) of the housing, respectively, said first and second internal cavities (10, 11) being open towards the base portion of the housing; wherein said plurality of reflecting surfaces comprise first and second reflecting surfaces (10a; 11a) which border with the first and second internal cavities (10; 11) of said appendages (4; 5) containing air; and wherein the first reflecting surface is interposed between the first optoelectronic device and the first internal cavity, and wherein the second reflecting surface is interposed between the second internal cavity and the second optoelectronic device, wherein said optical path extends in a plane at an angle to the longitudinal directions of said appendages (4, 5). a housing including a base portion and first and second hollow appendages (4, 5) in the form of fingers extending from the housing along respective longitudinal directions and at least partially facing one another, wherein in use said fluid is present between said first and second appendages (4, 5), first and second optoelectronic devices (13, 14) capable of transmitting and receiving radiation, respectively, mounted in a housing cavity (6, 7, 8; 19) formed in the housing, in the first and second appendages (4, 5) of the housing respectively, said housing cavity (6, 7, 8; 19) being open towards the base portion of the housing; the arrangement being such that in use a radiation beam transmitted by the first optoelectronic device propagates in an optical path which includes a portion crossing the fluid between said appendages (4, 5) and reaches the second optoelectronic device; wherein said optical path comprises a plurality of reflecting surfaces (10a; 11a; 21a; 22a) adapted to deflect the radiation beam between the optoelectronic devices (13; 14) and said fluid crossing portion, said reflecting surfaces (10a; 11a; 21a; 22a) being made integrally with said appendages (4, 5) of the housing; whereby first and second internal cavities (10, 11) are formed in distal portions of the first and second appendages (4, 5) of the housing, respectively, said first and second internal cavities (10, 11) being open towards the base portion of the housing; wherein said plurality of reflecting surfaces comprise first and second reflecting surfaces (10a; 11a) which border with the first and second internal cavities (10; 11) of said appendages (4; 5) containing air; and wherein the first reflecting surface is interposed between the first optoelectronic device and the first internal cavity, and wherein the second reflecting surface is interposed between the second internal cavity and the second optoelectronic device, wherein said optical path extends in a plane at an angle to the longitudinal directions of said appendages (4, 5).