For marketers in particular, beacons are important because they allow more precise targeting of customers in a locale. A customer approaching a jewelry counter in a department store, for example, can receive a message from a battery-powered beacon installed there, offering information or a promotion that relates specifically to merchandise displayed there. In a different department of the same store, another beacon transmits a different message. Before beacons, marketers could use geofencing technology, so that a message, advertisement, or coupon could be sent to consumers when they were within a certain range of a geofenced area, such as within a one-block radius of a store. However, that technology typically relies on GPS tracking, which only works well outside the store. With beaconing, marketers can lead and direct customers to specific areas and products within a store or mall. As a point of technical accuracy, the beacon itself does not really contain messaging; rather it sends a unique code that can be read only by certain mobile apps. Thus, the carrier of the smartphone has to have installed an app – and if he or she has not done so, no message will arrive. The choice to opt-out exists at any time. But the key to beaconing’s effectiveness is that the app does not actually have to be running to be awakened by the beacon signal.

http://blogs.hbr.org/2014/09/how-beacons-are-changing-the-shopping-experience/