If Conan was at all alarmed, you wouldn't be able to tell it from his expression. If anything, a stranger would guess that he was simply annoyed at the situation.

"What was the number? And what time did it arrive? There may be a clue in the timing." He pauses as he notes the officer's rather alarmed reaction. "I'm the Sleeping Kogoro's assistant," he offers in a rather unconvincing explanation. "I've seen a lot of bomb cases before. There is usually some kind of hint in the notice to further clues."

Eva's exclamation gets a rather irritated reaction. "Language. Shouldn't you be trying to set an example?"