No Cellphones
Although this may sound like common knowledge, there is more to the story. For information security reasons, non-governmental electronic devices are not allowed near submarines when they are at port.
There is a specific container (outside the submarine) where sailors may leave their cell phones. On the other hand, certain electronic items are permitted at sea but are strictly prohibited in some regions of the boat. Given that foreign powers may readily hack cellphones, they are not allowed aboard submarines.