Geofencing explained: how location-based arrival alerts work

A geofence is a virtual circle drawn around a real place. Cross into it or out of it and something happens — a reminder fires, a notification pings, a status updates. It is the quiet technology behind "you have arrived" messages and location-based reminders.

What a geofence is

Picture a pin on a map with a circle around it: a centre point (a place you care about) and a radius (how close counts as "here"). That circle is the fence. Anything inside it is "at" the place; anything outside is "away."

How arrive and leave detection works

The logic is simpler than it sounds. A device knows roughly where you are, and it knows the centre and radius of the fence. It measures the distance between the two:

• Distance drops below the radius → you have arrived.
• Distance rises back above it → you have left.

The alert fires on the transition — the moment you cross the line — not continuously while you sit inside.

Everyday uses

• "Remind me when I get home" or "when I leave the office."
• A nudge when you reach a shop so you do not forget the one thing you went for.
• Knowing when a family member you are sharing with arrives somewhere.

Foreground vs background

An honest caveat: in a browser, geofence checks happen while the page is open (the foreground). A true always-on geofence that wakes your phone in the background is the job of a native app — which is what the My Location Android app adds.

Set one up in My Location

On the web you can save a place, turn on an arrival alert for it, and pick a radius. While the app is open, you get a notification when you arrive at or leave that spot — and the check runs on your own device, using a position you already shared with the page, not a server. See the features page for the full toolset, or open the map to start.