Stock Price Alerts Must Track State, Not Just Thresholds

A stock API can supply prices for an alert, but it does not decide when a notification should be sent. A reliable alert needs a defined observation type, a trigger rule, remembered state, and a plan for missing data. In a synthetic example of five price updates, a simple above-$100 check matches three times, while detecting an upward crossing yields two events. Tracking whether the price has crossed the threshold prevents repeated updates above it from triggering repeated alerts. The article recommends defining the rule explicitly and describing its behavior in the interface so users can understand why notifications occur or do not occur.