The Internet of Things helps to have every individual interconnected with their surroundings and to interact with them through smart devices. In recent years, Bluetooth Low Energy (BLE) technology has become very popular in smart infrastructures, the medical field, the retail industry, and many more areas due to its availability in a plethora of wireless devices. BLE is widely used in IoT devices, such as smartphones, smart watches, and BLE beacons. Beacons are small, low-cost, and low-power wireless transmitters that bring attention to their location by broadcasting a signal with a unique identifier at regular intervals. BLE beacons are a promising solution for many smart city applications, from proximity marketing to indoor navigation. However, they do pose security and privacy challenges. This work discusses the characteristics of BLE beacons, the applications that can benefit from them, and the challenges they pose while trying to identify research opportunities and future directions.