How to announce that a website has no screen reader support?

We can use <noscript> to say Sorry, this website requires JavaScript to run.

What's the analogous way to announce that the site doesn't support screen readers? Something like <noscreenreader>Sorry, ...</noscreenreader>.

(Short backstory: it's an app dependent on the idea to never use words. It heavily relies on images to convey information. It wouldn't make sense to announce anything in spoken language.)

Solution

Screen readers work on top of the browser so there is no straightforward way (just some convoluted Flash techniques) to detect when somebody is using one.

Your best bet is to place the warning at the beginning of the content and to hide it for sighted users. This article mentions several techniques.

.hidden {
  position: absolute;
  left: -10000px;
  top: auto;
  width: 1px;
  height: 1px;
  overflow: hidden;
}

<div class="hidden">Sorry, this website requires JavaScript to run.</div>