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.
Format
Devicekey is a string like below.
12345678&5f4fd05f4fd07ebbb7275f4fd08a6075f4fd08a60267a35b2
Attention
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.