An analog circuit processes continuously varying voltages or currents directly, rather than turning the signal into software-managed data first. In a device such as a Geiger counter, it can amplify, filter, and shape sensor pulses with very little interpretation in the loop.
In cyber security, analog design matters because it affects how much you can trust a measurement before any code runs. Fewer software layers can mean a smaller attack surface, but analog systems are still vulnerable to physical tampering, component drift, electromagnetic interference, power glitches, and deliberate biasing of sensors or comparators. Defenders use shielding, filtering, calibration, and test points to make abnormal behavior easier to detect and troubleshoot.