Many contemporary technical elements (such as railings, light switches, power sockets, security cameras, etc.) have a very different aesthetic from the historical interiors to which they are added. Their placement in historical architectural interiors raises the question of their visibility and their power to disrupt the visual unity of an indoor space. Using logical argumentation and knowledge from the psychology of perception, a phenomenon from the discipline of architecture — the phenomenon of the perception of these elements — was analysed. Logical analysis showed that these additions do not disturb the harmony of the interior and that it does not lose its historical character. The conclusion is that their presence in the field of vision is not a radical interference with the monument.