Accessories and necklaces falsely claiming to "protect" people from 5G mobile networks have been found to be radioactive.
Netherland's authority for nuclear safety and radiation protection (ANVS) issued a warning about ten products it found that gave off harmful ionising radiation.
ANVS urged people not to believe in the false claims and use the products, which could cause harm with long-term wear.
The products identified included an "Energy Armor" sleeping mask, bracelet and necklace.
A bracelet for children, branded Magnetix Wellness, was also found to be emitting radiation.
Rampant conspiracy theories have fuelled a market of pseudoscientific "anti-5G" devices.
There is no evidence that 5G networks are harmful to health.
The World Health Organisation says 5G mobile networks are safe, and not fundamentally different from existing 3G and 4G signals.
Mobile networks use non-ionising radio waves that do not damage DNA.
However, there have been attacks on transmitters by people who believe they are harmful.