AIS -Cheap VHF Ship Alarm

Hardware required: A VHF Turn your VHF on and set it to channel 87 or 88. So you also monitor channel 16 press the dual scan button. Turn the volume up and set the squelch to fine. A burst of sound will tell you that a ship is within VHF range. It’s as simple as that.
See http://www.bebinka.net/misc/ais_system/index.htm