Android: How do bluetooth UUIDs work?
The UUID is used for uniquely identifying information. It identifies a particular service provided by a Bluetooth device. The standard defines a basic BASE_UUID: 00000000-0000-1000-8000-00805F9B34FB.
Devices such as healthcare sensors can provide a service, substituting the first eight digits with a predefined code. For example, a device that offers an RFCOMM connection uses the short code: 0x0003
So, an Android phone can connect to a device and then use the Service Discovery Protocol (SDP) to find out what services it provides (UUID).
In many cases, you don't need to use these fixed UUIDs. In the case your are creating a chat application, for example, one Android phone interacts with another Android phone that uses the same application and hence the same UUID.
So, you can set an arbitrary UUID for your application using, for example, one of the many random UUID generators on the web (for example).
It usually represents some common service (protocol) that bluetooth device supports.
When creating your own rfcomm server (with listenUsingRfcommWithServiceRecord), you should specify your own UUID so that the clients connecting to it could identify it;it is one of the reasons why createRfcommSocketToServiceRecord requires an UUID parameter.
Otherwise, some common services have the same UUID, just find one you need and use it.
See here
In Bluetooth, all objects are identified by UUIDs. These include services, characteristics and many other things. Bluetooth maintains a database of assigned numbers for standard objects, and assigns sub-ranges for vendors (that have paid enough for a reservation). You can view this list here:
https://www.bluetooth.com/specifications/assigned-numbers/
If you are implementing a standard service (e.g. a serial port, keyboard, headset, etc.) then you should use that service's standard UUID - that will allow you to be interoperable with devices that you didn't develop.
If you are implementing a custom service, then you should generate unique UUIDs, in order to make sure incompatible third-party devices don't try to use your service thinking it is something else. The easiest way is to generate random ones and then hard-code the result in your application (and use the same UUIDs in the devices that will connect to your service, of course).