In an increasingly connected world, where optical fiber networks dominate as a reliable communication medium, the possibility to sense environmental vibrations using the already deployed infrastructure represents a crucial and cost-effective feature that could revolutionize the way fiber infrastructures are conceived, shifting them from passive transport systems to active and responsive networks, opening new areas of application for Telco operators. This research area has been active since the last decade in both academic and private sectors, and continues to refine its methods in order to achieve this ambitious goal. Telco operators have already field-trialed optical sensing solutions in transoceanic submarine links (for instance to detect earthquakes and tsunamis) and are now considering extending optical sensing also in terrestrial networks.