Sensors

Why Your Phone’s Compass Can Point the Wrong Way

A map app can know your location correctly while the direction arrow points sideways. A compass app can also appear accurate in one place and drift badly in another. These problems make more sense once you separate two questions that phones answer in different ways: Where am I? and Which way am I facing? Satellite navigation can help answer the first question. To estimate the second while you are standing still, a phone commonly relies on magnetic and motion sensors. Those sensors are useful, but the magnetic one can be disturbed by ordinary objects around you.