The diffusion of Industry 4.0 within companies depends on their size. The resources and processes of large companies are more structured, so they are likely to deploy 4.0 technologies more quickly than SMEs. In order to prevent these SMEs from becoming victims of this industrial revolution, it is essential to fully understand the organizational, human and technological challenges of Industry 4.0. This article presents a review of the barriers and problems that a 4.0 investment can create for small and medium-sized businesses depending on their sector. Our analysis proposes a synthesis matrix with the effects of industry 4.0 in the different sectors of SMEs. This matrix presents the impacts, opportunities and risks of each of the main technologies of industry 4.0. Based on process innovations such as training plans or customer proximity, SMEs seem to have adopted their own Industry 4.0 concepts according to their sectors of activity.