In 2001, I put a Post-It Note on the back of my monitor: green for I can be interrupted, yellow for trying to work, pink for "heads down, don't bother me." In 2024, there's a $189 version with built-in app support: busy.bar

Busy Status Bar — Productivity Multi-tool Device with an LED pixel screen

Displays a personal busy message. Built-in Pomodoro timer and Apps. Fully customizable, open-source, and hacker-friendly

busy.bar

Civilized! In 2001 I worked for an art gallery that was open to the public, so headphones weren’t an option. We called my little Post-It system "VODC" or Virtual Office Door Closed.