iPhone (Safari) — tap the Share button at the bottom (the square with the arrow),
scroll down, tap
Add to Home Screen, then
Add.
Android (Chrome) — tap the three dots at the top right,
tap Add to Home screen (or Install app), then Add.
It opens full-screen with no address bar and
remembers who you are. It is a shortcut, not an app store download — nothing to install and
nothing to update.
It still cannot buzz your phone when you are
up. Keep the room open, or have someone text you.