Historical clue formulations

• [Is this thing on?] — 2025-09-03
• [Is this thing on?] — 2023-01-08
• Mic check noise — 2022-04-03
• [Is this thing on?] — 2021-06-11
• [Testing, testing] — 2021-04-24
• Typist's sound — 2009-10-11