A fork watcher is like the early-warning siren in a coastal town that detects tsunamis. When a chain reorganization goes beyond a few blocks, or if a new fork emerges with non-standard blocks, the watcher sounds the alarm. Some watchers provide real-time alerts via email, SMS, or dashboards, helping node operators and miners quickly pivot if needed.

Developers and exchange operators rely on these watchers to freeze deposits or withdrawals when something suspicious happens, preventing double spends or orphaned block chaos. This level of vigilance is especially valuable during software upgrades or the activation of new consensus rules, as it can prevent nasty surprises when chain splits happen in the wild.