Checking your blood pressure at home? Not all devices have been validated to make sure they’re accurate.

Starting in February 2020, researchers checked the 100 best-selling blood pressure monitors sold on Amazon in 10 countries for a year. (Note: Some of the study’s authors had ties to companies that make monitors.)

Only 16 percent of U.S. upper arm cuff devices—and none of the wrist cuff devices—had been validated, according to websites that keep track of validation.

Validated upper arm cuff monitors were more expensive (around $65) than unvalidated monitors (roughly $30), but some U.S. validated devices were only about $40.

What to do

Buying a blood pressure monitor? Check validatebp.org to see which U.S. devices have been validated.