Probably the most common use-case of BLE Central-Peripheral is the communication model between a smartphone and a smartwatch. Smartwatches are becoming very popular in our world.

Their primary purpose is to give controls over various apps (such as WhatsApp, Messenger, and Facebook etc.) without taking out the smartphone. In most cases, smartwatch comes as an accessory for a smartphone as it is dependent on the phone to receive and send data. Some manufacturers are making standalone smartwatches, which brings their own sensors (such as Wi-Fi and GPS etc.) to reduce the dependencies from the smartphone.

In order to understand the initial communication between a smartphone and a smartwatch, we will consider a real life example of a Motorola 360 smartwatch and a Samsung Galaxy S7 Edge smartphone. When a smartwatch comes out of the box, it needs a connection from a smartphone. It broadcasts its identity to everyone in the proximity performing the typical peripheral behavior. At this point, any smartphone (or central) can initiate the connection request to the smartwatch.

Moto 360 first asks to download and install Android Wear on the smartphone in order to fulfil the connection process. Once the software is installed, the pairing process is started. Smartwatch broadcasts its identity as Moto 360 3LFJ, which is visible on the smartphone as well. Upon pressing it, smartphone and smartwatch both show a 7-digit passkey (such as 7066595) which needs to be confirmed by the user. This step helps the user to verify that the user is pairing correct smartwatch with the smartphone. The devices are now paired with each other.

This is the typical process of pairing a central to its peripheral. When both ends are properly paired with each other, the peripheral does not broadcast its identity publicly. Even if the peripheral is disconnected from the central, peripheral will only search for that particular central while ignoring all other centrals in the proximity.