The device ID is a 24-character long hexadecimal string, but it’s not printed on the package anywhere, as it’s intended to be kept relatively secret. It’s different from the SIM card ICCID.
If you have already configured your device and claimed it to your account, you can use https://build.particle.io, select the Device tab (the circle with the lines, the target icon), then select the device. It will list the device ID.
If you have not set up your device yet, the easiest way to deal with the device ID is to use the Particle CLI, Command Line Interface. It will be useful later on as you use your Photon or Electron, so it’s worth taking the time to set it up.
If you are using Windows, I recommend using the new Windows CLI installer:
For Mac and Linux, follow these instructions instead:
https://docs.particle.io/guide/tools-and-features/cli/photon/
Once you’ve installed the CLI, connect the device by USB to your computer and put the device in Listening Mode if it’s not already blinking blue. Hold down the SETUP button (MODE for Electron) until the status LED blinks blue.
Issue the command:
particle identify
This should list the device ID.