One idea is to let the guest put his device in a faraday cage, locked, and bring the cage into the room. The key of the cage would be kept at the counter acces

One idea is to let the guest put his device in a faraday cage, locked, and bring the cage into the room. The key of the cage would be kept at the counter accessible to the guest also in a self-serve manner. So the guest will know he has his device with him, but cannot use it during his stay.