diff --git a/README.Rmd b/README.Rmd
index 57e9cfa..11a7f6b 100644
--- a/README.Rmd
+++ b/README.Rmd
@@ -109,6 +109,8 @@
 
 -   `'s'` enable presentation mode with speaker notes when the Notes plugin is activated
 
+On mobile browsers (touch devices), a speech-bubble button next to the fullscreen button overlays the current slide with its speaker notes -- useful for practicing a talk on a phone or tablet, where the separate speaker view window of the `'s'` shortcut is awkward. The overlay shows the slide title, its planned time (if annotated with a timing comment), and the notes, and follows along as you change slides. It appears only if the deck contains notes at all.
+
 -   `'m'` enable menu mode when the 'menu' plugin is activated
 
 Pressing `Esc` exits all of these modes.