6. Inertial sensors
If you go into a place where no wireless system works, inertial sensors can keep track of your location based on other inputs. Most smartphones now come with three inertial sensors: a compass (or magnetometer) to determine direction, an accelerometer to report how fast your phone is moving in that direction, and a gyroscope to sense turning motions. Together, these sensors can determine your location with no outside inputs, but only for a limited time. They'll work for minutes, but not tens of minutes, Broadcom's Abraham said. The classic use case is driving into a tunnel: If the phone knows your location from the usual sources before you enter, it can then determine where you've gone from the speed and direction you're moving. More commonly, these tools are used in conjunction with other location systems, sometimes compensating for them in areas where they are weak, Abraham said.
Outdoor navigation on a sidewalk or street typically happens on one level, either going straight or making right or left turns. But indoors, it makes a difference what floor of the building you're on. GPS could read this, except that it's usually hard to get good GPS coverage indoors or even in urban areas, where the satellite signals bounce off tall buildings. One way to determine elevation is a barometer, which uses the principle that air gets thinner the farther up you go. Some smartphones already have chips that can detect barometric pressure, but this technique isn't usually suited for use by itself, RX's Roy-MacHabee said. To use it, the phone needs to pull down local weather data for a baseline figure on barometric pressure, and conditions inside a building such as heating or air-conditioning flows can affect the sensor's accuracy, he said. A barometer works best with mobile devices that have been carefully calibrated for a specific building, so it might work in your own office but not in a public library, Roy-MacHabee said. Barometers are best used in combination with other tools, including GPS, Wi-Fi and short-range systems that register that you've gone past a particular spot.
Sometimes just detecting whether someone has entered a certain area says something about what they're doing. This can be done with short-range wireless systems, such as RFID (radio-frequency identification) with a badge. NFC (near-field communication) is starting to appear in phones and could be used for checkpoints, but manufacturers' main intention for NFC is payments. However, shopper loyalty company Shopkick is already using a short-range system to verify that consumers have walked into a store. Instead of using a radio, Shopkick broadcasts ultrasonic tones just inside the doors of a shop. If the customer has the Shopkick app running when they walk through the door, the phone will pick up the tone through its microphone and the app will tell Shopkick that they've entered. The shopper can earn points, redeemable for gift cards and other rewards, just for walking into the store, and those show up immediately. Shopkick developed the ultrasonic system partly because the tones can't penetrate walls or windows, which would let people collect points just for walking by, CTO Aaron Emigh said. They travel about 150 feet (46 meters) inside the store. Every location of every store has a unique set of tones, which are at too high a frequency for humans to hear. Dogs can hear them, but tests showed they don't mind, Emigh said.