Passengers will be able to use their devices right up to boarding time. After that, Emirates staff will take gadgets that are larger than a smartphone, and wrap them in bubble wrap.
They are then secured in tamper-proof boxes, and stored in the cargo hold. Once travellers have landed in the US, they must proceed through customs as normal. They can pick up their gadgets from the baggage claim, after presenting their boarding pass and ID to a member of staff.
(Source: CEO Middle East YouTube channel)