A magnetometer senses the Earth's magnetic field, which is present everywhere all the time, and notes anomalies in the field caused by the presence of materials regardless of whether they have magnetic properties.
The devices are thousands of times more sensitive than an airport metal detector.
Breiner used the magnetometers to help archaeologists search deep below the ground or water, joining explorers looking for sunken ships off the coast of California and Mexico.
He also helped discover the ruins of Sybaris, an ancient city in Southern Italy, as well as more than 100 ancient artifacts from the Olmec civilization in Mexico, which existed between 1200 and 400 B.C.
Breiner was one of six people chosen as winners of the 2014 Lowell Thomas Award from the New York-based Explorer's Club, founded in 1905 to honor "explorers of the planet."
The club cited his work in discovering "ancient objects hidden from view by the ground or the sea using magnetometers."
Among his discoveries cited in the award was a 400-ton Spanish galleon that may have run aground off the coast of Baja California on a return trip from China with a cargo that included silk, beeswax and Ming Dynasty porcelain.
Others receiving the award included astronauts Buzz Aldrin and Kathryn Sullivan, deep-sea explorers Robert Ballard and David Gallo, mountaineers Sir Edmund Hillary and Barbara Washburn, and naturalists Dian Fossey and Sir David Attenborough.
Breiner sold Geometrics in 1976, but continued leading the company until 1983, when he founded Syntelligence, an artificial intelligence company that designed software for banking and insurance underwriting.
He later helped found Quorum Software Systems, which built software that allowed Apple applications to work with hardware made by other companies.
While he was at Stanford he worked for Varian Associates, a Palo Alto company that made electromagnetic equipment, and he stayed at that firm until he founded Geometrics.
While at Varian, he demonstrated the use of a magnetic device for detecting weapons, which was used by the U.S. government to find a hydrogen bomb that had fallen into the ocean off the coast of Spain in 1966.
Besides his business ventures, Breiner was co-founder of of the Peninsula Open Space Trust and, with Mimi Breiner, established an endowment to support scholarships for Stanford students in geophysics.
He also served as chairman of the Geologic Safety Committee for Portola Valley, which lies on the San Andreas Fault.
The fault was an attraction, if anything, to Breiner when he moved to Portola Valley in the 1960s, and he had a seismograph in the basement of his home, according to a 2002 article in The Almanac.
"I don't worry about earthquakes. I chase them. They're fascinating," he told The Almanac.
Breiner kept close track of earth movement and faults, and enjoyed comparing archive photographs from after the 1906 earthquakes on the San Andreas Fault with images that he took himself; he located the site where the fault ruptured 6 feet across Alpine Road, according to the story.
Breiner gave well-received presentations about earthquakes to students at Corte Madera School in Portola Valley, and to Portola Valley's Nature and Science Committee about his work in archaeology and photography.
He was a distance runner who competed in 10 marathons, including the Boston Marathon, and enjoyed skiing, hiking, photography and travel.
He was especially skilled in photography, said Armand Neukermans of Portola Valley, a longtime friend.
"Sheldon was a unique individual, kind of the Indiana Jones of Portola Valley," Neukermans said. "He didn't invent the magnetometer, but he made good use of it."
Neukermans and Breiner were neighbors in the Ranch neighborhood in Portola Valley for about 20 years.
"He lived in Portola Valley for a very long time, from the time the Ranch was started," Neukermans said.
Born on Oct. 23, 1936, in Milwaukee, Breiner spent his childhood in St. Louis, Missouri, where his parents, Jewish immigrants from Eastern Europe, owned a bakery.
He entered Stanford in 1955 after the university offered to pay for his education if he studied earth sciences. He completed his doctorate in the field in 1967.
"If I'd have stayed in St. Louis, I would have had to fix the bakery equipment in my spare time," Breiner said in the 2002 story.
He met Mimi Farrington while at Stanford, and they were married in 1962. He is survived by Mimi; a son, David (Sharon Geaghan); a daughter, Michelle Driskill-Smith (Alexander Driskill-Smith); a brother, Richard (Dorothy); and five granddaughters: Charlotte, Meredith, Julia, Beatrix, and Elyse.
A community celebration of his life will be announced later, according to Mimi Breiner.
The family prefers memorial donations be made to the Peninsula Open Space Trust at openspacetrust.org/donate.
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