To communicate with the smartphone most of these fitness bands use Bluetooth Smart technology (also known as Bluetooth Smart) This means that the devices connect in a different way from regular Bluetooth. There is no pairing password because most wristbands do not have a screen and/or a keyboard. Most wristbands use a GATT ( Generic Attribute Profile) which means that every wearable device includes a set of services, each of which has a. set of. characteristics. In order to demonstrate this, I used some ready code from Android SDK, an example of an application that connects to Bluetooth LE devices.”]
Source: https://securelist.com/how-i-hacked-my-smart-bracelet/69369/