Bluetooth is a wireless personal area-networking standard for exchanging data over short distances. Bluetooth Low Energy (BLE) is the power and application-friendly version of Bluetooth that was built for the Internet of Things (IoT). The power efficiency and low energy functionality make this protocol perfect for battery-operated devices. Since BLE now comes native on every modern phone, tablet, and computer, it makes for a perfect starting point to connect with the vast multitude of devices that IoT promises to bring to the world. A Bluetooth device, like any wireless device, announces itself to the world, by sending out advertisement packets.
BLE advertisements are a periodic unidirectional broadcast from the peripheral to all devices around it. A listener can then use the information in these packets to gather the information being advertised or connect to the advertiser. Certain devices cannot be connected to, and this depends on what is announced in the advertisement header. The four types of advertisements are: