Monotonic countdown timer

Choose a duration or phases, or a target date and time with an explicit UTC offset (daylight saving time is not resolved automatically). Total time from 1 second to 7 days, up to 16 phases, 100 cycles and 1600 boundaries. Start, pause and reset. The visible elapsed time uses performance.now; the alarm uses Date.now. For a hidden tab, pause and resume manually, or use wall-time catch-up with at most one signal and a count of skipped phases. Clock and suspend differences are reported. Turn on the sound and test it yourself; autoplay rules, suspending or a closed tab may delay or lose it. There is no wake-up or delivery guarantee. This is a local browser observation only: no hardware diagnosis and no universal accuracy. Nothing is stored, recorded or uploaded, and no private-data telemetry is sent. Stop or reset clears the session. Browser, OS or permissions may leave results UNKNOWN.

Inputs stay in this tab and are not uploaded or saved automatically. Optional aggregate usage counts and coarse processing diagnostics are sent only after consent, without input content or filenames. Clearing or closing loses inputs; save needed outputs first.

Try a short countdown with pause, resume and reset. Check the hidden-tab setting you chose before you rely on the elapsed time.