antimagnetic
adjective
an·ti·mag·net·ic 
ˌan-tē-mag-ˈne-tik,
ˌan-ˌtī- of a watch
: having a balance unit composed of alloys that will not remain magnetized
Example Sentences
Recent Examples on the Web They are all made from a derivative of silicon, called Silinvar, which is known for being lightweight, rugged and antimagnetic. 
Paige Reddinger, Robb Report, 6 Apr. 2022 The brand was the first to develop the inner iron case to protect the movement and make the watch antimagnetic. Roberta Naas, Forbes, 25 Feb. 2021 Brands typically make watches antimagnetic in two ways: using materials like silicon, which don’t conduct a magnetic charge, or enclosing the movement in a soft-metal case. Rachel Felder, New York Times, 1 May 2020 In 2013, the brand introduced an antimagnetic version of its Seamaster Aqua Terra, which did not cage its movement but still promised to resist magnetization up to 15,000 gauss. Rachel Felder, New York Times, 1 May 2020
Paige Reddinger, Robb Report, 6 Apr. 2022 The brand was the first to develop the inner iron case to protect the movement and make the watch antimagnetic. Roberta Naas, Forbes, 25 Feb. 2021 Brands typically make watches antimagnetic in two ways: using materials like silicon, which don’t conduct a magnetic charge, or enclosing the movement in a soft-metal case. Rachel Felder, New York Times, 1 May 2020 In 2013, the brand introduced an antimagnetic version of its Seamaster Aqua Terra, which did not cage its movement but still promised to resist magnetization up to 15,000 gauss. Rachel Felder, New York Times, 1 May 2020 Word History
First Known Use
1883, in the meaning defined above