The growing range of sensors in measuring systems is discussed. It is suggested that many potential application areas exist for these types of sensors. The multiplexed sensors are divided into two types, three-axis 'vector' sensors and sensor arrays. System requirements for each of these are different. For the vector sensor, magnitude and direction information are required and three systems are the maximum number to be multiplexed. Parameters such as magnetic field, acceleration and rotation rate fall into this category. Sensor arrays are typified by the hydrophone application. Distributed sensors based upon POTDR have found application in the power generation industry. With this technique the current passing through large conductors can be measured. Considerable interest is also being shown in the use of distributed sensors for intruder location and for security systems in general. In all of these examples the advantages of the optical fibre make the sensor a viable approach