Can I use wifi to broadcast a message containing plaintext, so any device nearby can receive it, even they are not mutually connected/authenticated?

Can I use wifi or Bluetooth to broadcast a message containing plaintext (like “How are you?”), so any device nearby can receive it, even they are not mutually connected (authenticated)? --I know normally devices need to be connected/paired before they can exchange or share information. Here I am curious if there's a way to broadcast through wifi or Bluetooth hardware, in the old way like a radio station. So one device sends out information, and any nearby device can read it. Appreciate any feedback.

Question by Sung T on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.