Smell
Techfolk don't quite believe smell is real, because if you're a non-smelling entity, it sounds like made-up bullshit. You're telling me you can detect microscopic floating particles in the air? And you can tell if something was here recently from the smell it left behind? It sounds like some crystal hippy aura nonsense.
(And this is before we get onto the fact that at a quantum level, smell is sound. As the scent particles strike your scent receptors, the receptors pick up the resulting resonance.)
I like to imagine techfolk gently trying to trick a human into revealing that they're just making up this ability. The human adds a scent diffuser to their living space, so the techfolk coat the bottoms of the diffusion sticks with wax so they can't take up any liquid. The techfolk are bewildered when the human does notice the lack of smell! The human must have secretly seen them applying the wax…
The techfolk think they've caught the humans out when the humans' descriptions of smells don't match. The humans claim that even though there are around 400 types of human scent receptors, each human has only about 150 of these, so a bunch of different humans will detect different scents. Convenient…
The techfolk keep bringing blindfolded humans things to identify by smell, and are frustrated when the humans keep getting it right every time. Either the humans aren't bullshitting, or they're really committed to the bit, and the techfolk aren't sure which one is more unbelievable.