A barometer is an instrument used to measure atmospheric pressure. Traditional barometers use mercury or a sealed chamber, while modern versions often use electronic sensors. Because air pressure changes with weather, altitude, and movement, a barometer is useful for detecting environmental change rather than just giving a single static reading.
In cyber security, a barometer matters as a practical example of state-sensitive observation: some clues only appear when a system is under motion, stress, or changing conditions. Defenders use the same idea when monitoring logs, sensor data, and device behavior for anomalies during transport, failover, or reconfiguration. Attackers may also exploit unstable or unusual states to hide activity or trigger faults, so recognizing pressure-like signals can help analysts distinguish normal variation from suspicious change.