Off-route warnings (a PRO+ feature) fire when all of these are true: you started the route with Start Navigation, you’ve moved more than 200 m from the trail (that’s the default — adjust it at Home > Settings > App Settings > Customise > Off route warnings, or from the map options while navigating), and HiiKER has notification permission on your phone. They’re push notifications, so you won’t hear one if your phone is muted. They don’t trigger when walking the route in reverse, and after one fires it won’t repeat until you’re back on the route. Good way to test: plot a short route near home and deliberately walk 200 m+ away from it.