HOW THE SYSTEM WORKS Tiny electronic components that increasingly come standard with smartphones are capable of measuring air pressure with great accuracy. Inside the sensor, there is a flexible membrane exposed to air on top of a vacuum chamber. Air pressure pushes down and deforms the membrane. The sensor est-mates barometric data based on how much the membrane bends. The phone’s sensor measures the value of air pressure and determines how high the user is, the “z” coordinate. Other location technologies, by estimating the distance from the nearest cell towers, for instance, calculate the device’s longitude and latitude, the “x” and “y” coordinates.The data is sent to a remote server that compares it with sophisticated atmospheric models to determine a pre-cise, three-dimensional location. Elevated position Elevated Ground Ground level More pressure Pressure Membrane BAROMETRIC-PRESSURE SENSOR Bent membrane Reading Vacuum chamber Elevatedposition Ground

SOURCE: Bosh and Polaris Wireless. GRAPHIC: Alberto Cuadra and Craig Timberg - The Washington Post.