Carbon fiber knives can indeed be detected by modern metal detectors, but so can titanium, zippers, eyelets, buttons, candy wrappers and many other seemingly objects and materials – but these are almost never (or ever) detected in a scan in live scenarios.
This is because scanners are set to ignore or are on a lower sensitivity level so they can detect only potentially dangerous or otherwise non-permissive items: a firearm or a standard knife which has high levels of mass and volume of steel.
Otherwise these detectors, when used for real world applications, would be impractical and inefficient as it would detect and disrupt security protocols for harmless objects and materials that’s both in our bodies and on our persons.
I’ve been equipping carbon fiber weapons and tools for over a decade across the world through airports, government buildings and other high security facilities with not a single detection or incident.
However, my kits are as small as usefully possible using the least amount of raw material needed.
This is because the purpose of non-metallic knives and impact tools are for extreme covert carry and used for special circumstances. Avoiding metal detection is just one aspect, passing physical searches is just as important – hence the minimal mass and volume.
They are not “real” knife replacements and should not be considered as one. And so large and thick carbon fiber weapons should not be considered as covert – as these can be easily found during a physical search and possibly through metal detectors.
However, if size is a concern, G-10 composites and “clean” ceramics are excellent alternatives.