If you set up a Nearby Alert, you will receive a notification when your friends are in or out of the zone. This zone is a radius around you, which you can change the range of at any time.
If a friend moves closer to you than the distance you set, you'll receive a notification that they are "in the zone." If they move further from the distance you set, you'll receive a notification that they are "out of the zone."
To set the nearby alert, follow the steps below:
Menu (upper left) - Nearby Alerts - Select Radius - Save
In addition, if you want to receive a Nearby Alert but are coming too often, you can narrow the radius. (ex: 5 miles → 1 mile)