Detect Detection

For the duration, you immediately know if anyone within 60 feet of yourself is casting or concentrating on any of the following spells: Detect Evil and Good, Detect Magic, Detect Poison and Disease, or Detect Thoughts. If you sense any of these spells, you know which spell it is and can take the Magic action to see a faint aura around the creature casting it. Seeing this aura also grants you a superficial insight into the creature's reason for casting their spell, which the DM communicates to you with a single word, such as "traps" or "illusions."

The spell is blocked by 2 feet of stone, dirt, or wood; 2 inches of metal; or a moderately thick sheet of lead.