The device doesn’t need to be claimed to come online, and you don’t need to be at the device to claim it.
In order to add a device to another developer account, you need to be able to log into the other account. If you have the account credentials, you can just log in and claim the device by Device ID even if the device is elsewhere, as long as it’s powered on and breathing cyan.
For products only
Most cellular products claim devices to a single account owned by the product owner, so there’s no need to have other credentials.
Product devices can be claimed to the owner or team member account even if the device is offline, as well.
Some cellular products that do not need to receive events on the device can operate in product/unclaimed mode. You never claim the device at all, and it will still receive product firmware updates, and can receive function and variable requests, and can send product events.
Some cellular products use customer accounts and claiming, and that still requires that the device be online and breathing cyan, however product customer accounts can use two-legged shadow customer impersonation so you don’t need to manage account credentials for each account.