Universally Unique IDentifier

A 128 bit string guaranteed to be unique usually displayed is an 8-4-4-4-12 digit hexadecimal string for example: d444840-9dc0-11d1-b245-5ffdce74fad2

RFC 4122

Types generated using:

  1. a timestamp and the MAC address of the computer on which it was generated.
  2. random numbers

Nordic Semiconductor

LED Button Service (LBS)

00001523-1212-EFDE-1523-785FEABCD123 LED Button Service (LBS)
00001524-1212-EFDE-1523-785FEABCD123 Button Characteristic
00001525-1212-EFDE-1523-785FEABCD123 LED Characteristic Write data to the LED Characteristic to change the LED state.

Alexa Gadgets Service


2BEEA05B-1879-4BB4-8A2F-72641F82420B RX Characteristic
F04EB177-3005-43A7-AC61-A390DDF83076) TX Characteristic
Nordic UART Service (NUS) custom service

6E400002-B5A3-F393-E0A9-E50E24DCCA9E RX Characteristic
6E400003-B5A3-F393-E0A9-E50E24DCCA9E TX Characteristic

Unique Device Identifier

A sequence of 40 hexadecimal digits that uniquely identify an device to an Apple device. It is derived from hardware details including MAC address (which Apple has choosen to obscure).
This is a non-persistant value, that is it will change. For example if there is a bluetooth device which is currently known to a Mac Bookpro as of 7f47842aaefc441b91a83ce5ba1b4fd7 (which happens to have a MAC address ending with E4CE) after a boot of the Mac Bookpro the bluetooth device will be know with a DIFFERENT value for example 8d65ba20ef4842eb8bce8a68a1cef5c7 !
Additionally a different Apple device will know the same bluetooth device by a different UDID!

See SourceFuse.com/blog

Apple has depracated the UDID (Unique Device IDentifier) for apps , considering it a privacy concern, and no longer accepts apps that use it.