Sentinels
A sentinel is a person or thing that stands guard to observe and report, serving as an early warning against danger. Historically, sentinels were stationed in military outposts, city walls, or fortifications to monitor for enemies and to signal alarms. The term is used broadly across disciplines to denote a guiding or precautionary watch.
In biology and environmental science, a sentinel (or sentinel species) is an organism used to detect risks
In computer science and information technology, sentinel concepts anchor control flow and data boundaries. A sentinel
Other uses include security and monitoring contexts, where sentinel devices or alarms act as watch points,