You mean your sailboat should have one, right? Or, the ship....
The sailboat must have various types of radar alarms for solo voyaging. The skipper simply has to sleep. When approaching and in shipping lanes, this becomes very dangerous. A ship’s radar is set to see land and other ships. Even with a “radar reflector” up in the mast to enhance a sailboat’s radar echo, ships commonly don’t “see” sailboats. I have seen the lights of a ship clearly at night, called them on VHF 16, and asked if the “see” me on radar, and often, they say no, even when I have my nav lights on and give them my GPS coordinates.
So the sailboat must at least have a “radar detector,” so when a ship’s radar signal is sweeping the sailboat, the radar will be detected, setting off an audible alarm to wake up the sleeping skipper.
In the middle of the ocean, it doesn’t matter much. I have literally gone for weeks at a time without seeing one single ship on the horizon or closer. But in shipping lanes, or tight areas like the Caribbean, you can see ten ships a day.