Devicekey is needed for obniz cloud to identify your device.
obniz Boards are having devicekey. It is written at it's factory. But when you install obnizOS to your device, it doesn't have a devicekey.
Devicekey can be issued from obniz cloud.
Devicekey is a string like below.
Please keep secret and never ever make this key public. You can download your devicekey on the cloud anytime.
You can't erase your devicekey after written. Erasing whole flash memory is only way to erase devicekey from your device.
You can't use same devicekey for two or more devices.