The first thing Sherlock is likely to notice about Conan is that the kid is hiding something. He's much more intelligent and observant than he would like everyone to believe, and often slips up in his attempts to convince everyone that he's just a smart kid. ESPECIALLY when there's a mystery around. He has a bad habit of tl;dring about various subjects and then backpedaling as he claims that he saw something about it on television. Even after speaking for several minutes on the history of obscure folklore traditions or some detailed chemical method in forensic science.

His body language and vocabulary tends to vary widely too, from childish and cutesy, to cool and confident. At times he borders on arrogant.

Conan is an avid soccer player, but his skills are far in advance of where they should be for a child his age. Likewise, his reading ability, general knowledge, and language skills are all far ahead of his apparent age. He plays the violin. Conan has perfect pitch, but no relative pitch at all. Because of this he can hear and identify tones, but is incapable of replicating them with his voice.

He prefers more formal clothing than most normal children. He is rarely seen without a jacket of some kind. Sport, athletic or formal. He wears glasses, but they are actually made out of clear bulletproof glass.

He has several scars, including a healed bullet wound on his stomach and a knife scar on his chest.