The unit comprises: a casing (1) with a protected interior, a window (2) closed by a transparent element (3) and support means (4) to carry an optical system (5) facing said window (2); image detection means (6) accommodated in said casing (1), facing said optical system (5), an associated with connection means with the exterior for the supply and/or bidirectional signal exchange; and heating means to provide thermal energy to said transparent element (3), or to an adjacent zone thereto, aiming at avoiding lacking transparency problems, due to ambient and climatic factors.