Geolocation needs internet connectivity to check your home’s current target temperature as you pass each geofence. If there’s poor connection (eg. no wifi and only GPRS data) at your set distances, the alerts won’t trigger. If that happens try switching on your mobile data if it’s off, or change your “away from” and “returning” distances to a location with improved connectivity.
Geolocation works even when the Hive app is closed, it’ll also work if you reboot your phone, with no need to launch the app. This is why you need to have Background App Refresh enabled for Hive as well. You can find this under your phone's Settings > General on your iPhone.
Geolocation has been designed to minimise any impact on your mobile’s battery. It only requests an approximate location, so in most cases your phone won’t need to switch on GPS, unless it can’t pick up the location in any other way (eg. if you’re in a rural location).
If more than one person in your home has the Hive app on their phone, they can use Geolocation too and set their own temperatures and distances to be notified at. Only the phone that’s crossing these set distances will receive an alert, so you won’t be notified unless you’re out and about.