Geolocation Api Demo  

Some devices have both a browser and a GPS, like your cell phone for example. You will be prompted to allow the browser to get to your position (once).
Note: If you have an Android phone (or tablet) with a GPS, and if you are using a Chrome browser on your laptop (that probably has no GPS), logged in with the same user as on your phone, this will work too. Chrome and Android are Google products, they can communicate... Same with another browser, but logged in your Google account.
Good to know, specially if you want to prevent it.