Ships that pass in the night no longer have to worry about collisions. Larry Anderson, president of Radar Devices Inc., based in San Leandro, Calif., has developed a device that works with radar to eliminate naval crack-ups.

Anderson's patented invention, the Guard Zone, attaches to conventional radar installed on the bridge of a ship. The Guard Zone continuously "reads" the radar, and when a target comes within a predetermined distance, it sounds an alarm.

Unlike humans -- who Anderson claims are responsible for 85% of all accidents at sea -- the Guard Zone "doesn't sleep, knock off for coffee, or turn away for a smoke," says its inventor.The Guard Zone attachments, which are the size of a shoe box, cost from $800 to $5,000. Radar Devices Inc. is also marketing a more advanced line of related products, including the Automatic Radar Plotting Aid (ARPA), which automatically tracks, plots, and projects the future position of targets.The ARPA costs from $28,000 to $55,000.

Anderson has relied on a series of limited partnerships to fund research and development. Production financing for his 75-employee firm comes from a commercial bank line of credit.

A former real estate salesman who took correspondence courses in electronics, Anderson founded his company in 1973 after a downturn in the California real estate market. While last year's sales were close to $1 million, Anderson expects orders for the more expensive ARPA equipment to boost 1982 sales to $10 million.

Although Anderson owns a powerboat himself, he only uses it for research and development. "I've been on it just for fun once in the past two years," says the 44-year-old former Navy man. "I'm too busy working my tail off on shore."