Truly Awake · even in the background
Asleep
Not holding the machine awake.
Works in the background — switch tabs or minimize freely. A faint locally-generated tone holds the system awake using no network. Raise the tone to confirm it's live. This stops the machine sleeping; the screen may still dim, and it won't change your chat-app status.
Audio couldn't start here
Some embedded frames block it. The always-works version with no install:
open a long video or radio stream on YouTube, keep it playing
(audio is enough — no need to watch), and it'll hold the machine awake.