Optical networks are spanning the world. They are the main medium for carrying all types of data-traffic. From a vulnerability and security perspective, it is therefore the most important part of the network to protect against any physical impacts that may cause disruptions or security incidents. In this paper, we demonstrate and describe a scalable, low-cost monitoring system based on detecting the state of polarisation in the fibre cables. We give examples on how any direct movement of fibre-cables or fibre-cords as well as indirect vibrations on the cable can be detected, and how basic characteristics in the patterns can be used for recognition of these events.