What Is a Sensor? A Discussion Paper

Sensors are among the most widely used tools created by humans, appearing virtually everywhere in our daily lives. They help us interact more effectively with our surroundings, especially as our natural senses alone can no longer fully meet modern demands. Sensors are also indispensable components of contemporary equipment and machinery. This is largely because most of today’s machines operate in closed loops: every action is monitored and adjusted in real time, and this control is made possible by sensors. The information a sensor provides cannot be independently verified in the moment except by other sensors. This is why people often say: no machine can perform better than its sensors. This leads to a fundamental question: Do we truly understand what this extremely important thing called a “sensor” is? We would confidently say yes—we know what a sensor is. But if we ask whether we can define a sensor in a clear and widely accepted manner, the answer becomes less certain. Looking around, we find a variety of different sensor definitions. Matters grow even more complicated when we consider specifications, terminology, and classifications. Even something as basic as the function of a sensor is frequently misunderstood. In short, the term “sensor” lacks precision in its meaning. In this paper, we present the current situation regarding sensor terminology and definitions. Our aim is to encourage discussion rather than impose a particular understanding or viewpoint. The paper is organized into four sections: (i) Sensor Definitions; (ii) Properties of Sensors: Practical Language Use; (iii) Classification of Sensors; (iv) Can Sensors Be Smart?