GPS does not function well indoors because satellite signals in the shop area are diminished by roofs, walls and other objects. Therefore, other solutions must be sought. Although these solutions function in a similar way to GPS, they feature favourable and small senders (Beacons) featuring a signal that covers large areas and can penetrate through walls (Bluetooth Low Energy). Many companies also install Wi-Fi signals to measure the frequencies and positions of customers. Google, Navizon and Skyhook are the leading companies in this area. Even better are combinations that use the sensors in a smart phone. These include the accelerometer, gyroscope and other sensors. They can also track orientation and enable information on what the customer is currently looking for in almost real time. This additional information helps determine whether the customer is currently in a purchasing mood. Those who selectively hurry through the shop area are supposed to be in a different mood to those who slowly rummage through shelves.