title: A "speedometer" that doesn't use GPS
body: <p>How to calculate speed without requiring GPS? I have heard of something called "sensor technology" but am not sure what that means. I am asking because I want to make an app, but I don't think it is battery efficient to use GPS, plus it is for a long-term project so I want the app to continuously run without having to manually turn it on or turn on GPS. </p>