An investigation has found that nearly half of headphones intended for children don’t reliably keep volume down to safe levels to prevent hearing damage, The New York Times reports. Many headphones marketed as “safe for young ears” and promising to provide “100 percent safe listening” had “design flaws that could allow a child to bypass their volume-reduction features easily,” proving that volume-limiting headphones are not the perfect solution many parents had hoped. The worst among the 30 pairs tested “produced sound so loud that it could be hazardous to ears in minutes,” with some relying on resistors within the cord to limit volume, which sometimes failed to work at all. The full results of The Wirecutter’s investigation are available on its website.