Night mode puts the clock on black in a dim color. The small move every minute (in night mode and full screen) keeps the same pixels from staying lit all night, which helps OLED screens. For the darkest result, also turn your screen brightness down.
Alarms only ring while this page is open and your device is awake. They can't ring if you close the tab, quit the browser, or the device sleeps; phones and tablets may also stop the sound when the screen locks or you switch apps. For a nightstand: leave this page open, plugged in, with Keep the screen on (it uses your browser's Wake Lock) and night mode. For anything important, use your phone's own alarm as well.
Settings, alarms and world clocks are saved in this browser on this device (localStorage). Nothing is sent anywhere.
Pick a face (digital, analog, flip or words), press the full-screen button, and leave the page open. Turn on Keep the screen on so the display doesn't sleep, and use night mode at night: a dim red, amber or grey clock on black, with a small move every minute so an OLED screen doesn't get a ghost of the digits. Night mode can switch itself on and off at set times. Keys: F full screen, N night mode, 1–4 faces.
No. A web page can only make sound while it is open, and phones and tablets usually pause a page when the screen locks or you switch apps. A computer that goes to sleep also stops it. If the device wakes up within 30 minutes of a missed alarm, it rings late; after that it tells you it was missed. Keep the page open with the screen on, and plug the device in. For an alarm you can't afford to miss, also set one in your phone's clock app.
It shows your device's own clock, which your operating system keeps in sync over the internet. This page doesn't check the time anywhere else. World clocks use your browser's time zone rules, including daylight saving time. The word clock rounds down to five minutes; the dots below it count the extra minutes.
For a countdown, stopwatch or Pomodoro, use timer.gripe. To convert a time between zones or find a meeting time, use timezone.gripe.