Is there anything that allows mobile phones to receive signals at sea?

Yes, you can use the international maritime satellite phone.

International maritime satellite telephone mainly refers to the telephone business between ships and shore and between ships through international maritime satellites. It is used for communication between ships and between ships and land, and can be used for call, data transmission and fax.

It is understood that the tariff standard of China Unicom's maritime satellite business is: Pacific Ocean, Indian Ocean 43 yuan/minute; Atlantic East, Atlantic West 53 yuan/min. There is no time-sharing discount for the time being. Need to open international functions! You can also consult the customer service hotline for details.