One fiber equals thousands of sensors!
With fiber optics, the fiber itself is the sensor. When a laser pulse is sent through a fiber optic cable, temperature and vibrations can be measured continuously along a standard telecom fiber with a high level of accuracy.
Distributed Temperature Sensing (DTS) and Distributed Acoustic Sensing (DAS) are fully distributed systems, sensing temperature and vibrations over the entire fiber length. That can measure up to several tens of kilometers.