What method is used to activate from sleep mode based on external events?

The correct choice is Event-Triggered Wakeup. This method specifically pertains to activating systems from sleep mode as a direct result of external events, such as sensor inputs or notifications from other devices. In the context of CPS (Cyber-Physical Systems), this approach enables the system to conserve energy by remaining in a low-power state until an important event occurs that necessitates immediate processing or response.

Using event-triggered wakeup is advantageous for systems that monitor conditions and require quick reactions, as it allows the device to remain inactive (and therefore save energy) until the conditions warrant reactivation. This enhances both the efficiency and longevity of the system.

The other choices represent different wakeup strategies that do not focus on external events in the same way. For example, condition-based wakeup may involve internal thresholds being met rather than external stimuli, while scheduled wakeup relies on time-based triggers rather than real-time events. Prompt wakeup suggests user-initiated reactivation, which is not aligned with the automatic response mechanism inherent in event-triggered wakeup systems.