How does a sentinel work?

Could you elaborate on the mechanism behind a sentinel's operation? I'm particularly interested in understanding how it safeguards and monitors various aspects of a system, be it financial transactions, network security, or any other critical operations. Additionally, how does it respond to potential threats or anomalies in real-time, ensuring the integrity and stability of the system it oversees? Lastly, are there any industry-standard practices or protocols that sentinels must adhere to in order to perform their duties effectively?