Sound fades in over a few seconds when you press play, and the timer ends with a long, gentle fade (up to two minutes).
Binaural beats need headphones: each ear gets a slightly different pitch. Isochronic tones pulse on and off and work on speakers. Some people find them relaxing or helpful for focus; the research is mixed, and nothing here is a medical treatment.
iPhone and iPad (Safari, and every iOS browser): live Web Audio stops when the screen locks or you switch apps, so this is on by default there. The page plays the live mix for the first few seconds, then switches to the rendered loop. Changing a slider goes back to live sound for a moment and re-renders. The sleep timer fades out on its own, but iOS may delay it by a few seconds when the phone is locked. The ring/silent switch doesn't mute it.
Android: on by default too, so it keeps playing behind other apps.
Computers: live sound keeps playing in background tabs in Chrome, Firefox and Safari, so this is off. Random events (drops, crackles, waves, thunder) never repeat live. In a 90-second loop, a rare event such as a thunderclap comes back every 90 seconds.