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DATETOOLS

Set an alarm for 3:00 pm

Already set for 15:00 in your own time zone. Press "Set the alarm" to arm it, and add weekdays if you want it to repeat.

Clock and alarms

Time nowEurope/Bucharest

The time is 20:50.

Repeat on

No repeat. This will ring once, in 18 h 9 min, at 15:00.

Leave this tab open. The alarm is held in this page, not on a server, so closing the tab cancels it. Browsers also block sound on a page you have never interacted with, which is why setting an alarm arms the audio.
Permalink datetools.com/alarm-clock/3-00-pm

What a browser alarm can and cannot do

This alarm lives in the page. It is not a notification, a service worker or an account, so it needs the tab left open, and closing that tab cancels it. Said plainly here because a clock that quietly fails to ring is worse than no clock.

Within that, it is built to be reliable. The alarm stores the instant it is due and checks against your device clock from a background worker, so a tab you have switched away from still rings on time rather than when you next look at it. The screen is kept awake while an alarm is pending, where the browser allows it.

Browsers refuse to play sound on a page nobody has touched, and some refuse again after long inactivity. Setting an alarm arms the audio inside that press, which is the moment the browser trusts. If it still refuses, the page says so rather than staying silent and hoping.

Repeats and the clock change

A repeating alarm resolves against the local calendar each time rather than adding twenty-four hours. That distinction matters twice a year: an alarm set for 07:00 stays at 07:00 through a daylight saving change, where an alarm built on a fixed interval arrives an hour early or an hour late. On the day clocks go forward, an alarm set inside the skipped hour rings at the first moment that hour exists.

Common alarm times

Each of these opens with the time already set.

Other tools

The time shown is your device clock, read through the browser's own copy of the IANA time zone database. Alarms are held in this page only. Nothing is sent to a server.

Browsers block sound until you interact, so test it once before you rely on it.