Many lighthouses are equipped with a horn to help guide ships sailing in foggy weather. These foghorns, which make their sound by quickly releasing compressed air, can be heard for distances of up to 13 km (8 mi). Ship captains can determine their position by identifying distinctive combinations of long and short horn blasts specific to each lighthouse. Some lighthouses are also equipped with radio beacons that transmit Morse code radio signals. These radio signals, which are distinguished by short (dot) and long (dash) combinations, have a range of up to 320 km (200 mi).