A sensor signal is the data stream produced when a device measures a physical phenomenon such as sound, light, motion, vibration, temperature, or radio energy. The signal may be analog or digital, but in either case it is the raw evidence a system uses before any filtering, classification, or alerting.
In cyber security, sensor signals matter because many defenses depend on them: acoustic detectors listen for machinery or drones, motion sensors detect intrusion, and RF monitors watch for unusual transmissions. Attackers may try to hide by reducing their physical signature, while defenders try to extract reliable patterns from noisy environments. The security challenge is to trust the signal without trusting it blindly, since sensors can be fooled by background noise, interference, spoofing, or poor calibration. Good systems validate the signal, combine multiple sensors, and compare readings against expected behavior before making a decision.