Clock FAQ
Answers about Clock, from setting an alarm to adding a city.
Last Updated: November 10, 2026
1. General Questions
Q1: What is Clock?
A1: Five time tools in one browser tab: a big digital and analogue clock with a full screen view, alarms that ring in the tab, a countdown timer, a stopwatch with lap times and a world clock for any city. Everything runs in your browser.
Q2: How much does it cost?
A2: Nothing. It is free, with no registration and no limit. Like every page on ZeroDataUpload, it is supported by advertising.
Q3: Do I need to install anything or create an account?
A3: No. Open the page in a modern browser (Chrome, Edge, Firefox, Safari or Opera) on a computer, tablet or phone. Your alarms and cities are kept in that browser, so there is nothing to sign in to.
Q4: Is anything I do uploaded?
A4: No. Every alarm sound is made in your browser, and your alarms, labels, cities and settings stay on your device and are never sent to a server. The page itself loads the site's ads and analytics, as every page on the site does; the Privacy Policy explains those, and what you do in the tool is never part of them.
Q5: Does it work without an internet connection?
A5: The page needs a connection to load. Once it is open, the clock, the alarms, the timer, the stopwatch and the world clock keep working without one: the sounds are made on your device and every city's time comes from the time zone rules built into your browser.
Q6: How accurate is the time?
A6: The clock shows your device's own time, which phones and computers set from the network. The page does not fetch the time from anywhere else, so if your device's clock is wrong, the page is wrong by the same amount.
2. Alarms
Q7: How do I set an alarm?
A7: Open the Alarms tab and press New alarm. Pick the time (it starts one hour from now), type a label such as Wake up if you like, choose the days it repeats or leave it as a one-off, pick one of five sounds and press Listen to hear it, then Save alarm. The line under Rings says how long until it rings.
Q8: Will an alarm ring if I close the tab or my computer goes to sleep?
A8: No. A web page can only ring while it is open in a tab and the device is awake. A closed tab, a laptop with its lid shut or a phone that has put the browser to sleep cannot ring. When you come back, the Alarms tab marks an alarm that could not ring as missed. For an alarm you must not miss, set one on your phone as well.
Q9: Why does the page ask me to click it once?
A9: Browsers keep a page silent until you have clicked, tapped or pressed a key on it since it opened. If an alarm is set or the timer is running and you have not touched the page since it opened (after a reload, for example), the alarm could only ring in silence, so a note asks you to click anywhere on the page once.
Q10: Does it ring while I work in other tabs?
A10: Yes, as long as this tab stays open. Browsers wake tabs that are out of sight less often to save power, so when you switch away the page sets one extra timer for the next alarm, and every check compares with the clock instead of counting ticks. A hidden tab can still ring a little late; the ringing window then says how late.
Q11: What happens when an alarm rings?
A11: A window covers the page with the time, the alarm's label and two buttons: Snooze 5 min and Dismiss (Esc dismisses too). The sound repeats until you choose; after five minutes of ringing the sound stops, and the window stays until you close it. Alarms due at the same moment ring together in one window. With notifications turned on, a message also appears when you are in another tab or window.
Q12: What does Missed mean on an alarm?
A12: The alarm's time came while the page could not ring: the tab was closed or the device was asleep. When the page is next open, an alarm found up to ten minutes late still rings; one found later is marked Missed at its time on the Alarms tab, and a message says so, instead of ringing hours late. The mark goes when the alarm next rings or when you change it.
Q13: How do repeat days and one-off alarms work?
A13: Pick days with the buttons Mon to Sun, or the quick choices Weekdays, Weekends, Every day and Once. A repeating alarm rings on each chosen day. A one-off alarm rings at the next time that comes and then turns itself off; a snooze keeps it on until the snoozed ring. Turn any alarm off and on with its switch.
Q14: What happens to an alarm in the hour the clocks skip or repeat?
A14: In places with summer time, one night a year skips an hour and another repeats one. An alarm inside the skipped hour, such as 2:30 when the clocks jump from 2:00 to 3:00, rings as many minutes later as the clocks jumped, at 3:30, and the line under Rings shows that time in advance. An alarm inside the repeated hour rings once, the first time that time comes round.
Q15: How many alarms can I set?
A15: Up to 50, each with a label of up to 40 characters. An alarm without a label is called Alarm. Delete one with its bin; Undo in the message brings it back.
3. Timer and Stopwatch
Q16: How do I use the timer?
A16: Set hours, minutes and seconds in the three boxes (or with their plus and minus buttons) and press Start, or tap a preset from 1 minute to 1 hour, which starts at once. The ring empties as the time runs out and the line under the time says when it ends. Pause, Resume and Reset do what they say; when it reaches zero it rings until you dismiss it.
Q17: What happens if I close the page while the timer is running?
A17: The timer keeps its end time, so it keeps counting while the page is closed. If you open the page again less than a minute after it ran out, it rings; later than that, a message says when it ended and the boxes get its length back for another go.
Q18: Can I add time to a running timer?
A18: Yes: +1:00 adds a minute while it runs or is paused, up to 99 hours, 59 minutes and 59 seconds in all. The ring takes the extra minute into account.
Q19: How precise is the stopwatch?
A19: It counts from your device's clock and shows hundredths of a second, redrawn with every frame of the screen. It is as precise as the moment you press the button. If the device's clock is changed while it runs, the time counted changes with it.
Q20: How do laps work?
A20: Press Lap (or L) while the stopwatch runs. Each lap shows its own time and the total, newest first, with the current lap counting at the top. From two laps on, the fastest lap is marked in green and the slowest in red. Up to 1,000 laps are kept.
Q21: Does the stopwatch keep running if I reload the page?
A21: Yes. It keeps the moment it started, so a reload, or closing and opening the page again, carries on from the right time. The laps are kept too until you press Reset.
Q22: Does the screen stay on while the timer runs?
A22: While the timer or the stopwatch runs and the page is in view, the page asks the browser to keep the screen on, where the browser allows it. It lets the screen sleep again when they stop.
4. World Clock
Q23: How do I add a city?
A23: Open the World tab and type a city or a time zone, such as Tokyo, Berlin or Asia/Kolkata, choosing from the list that appears if you like, then press Add. Or tap one of the popular cities. Each card shows the time there, the date, the difference from your time and whether it is already tomorrow or still yesterday. Up to 50 cities are kept.
Q24: My city is not in the list. What should I type?
A24: Time zones are named after one large city each, so a smaller city shares the name of a bigger one in the same zone. Type a bigger city nearby in the same country or zone, or the zone's name. Some well-known cities are understood directly: Mumbai, Delhi, Bengaluru, Chennai, Hyderabad, Pune and Ahmedabad all lead to India's time zone.
Q25: How does the world clock handle summer time?
A25: Every city's time comes from the time zone rules built into your browser, the same tz database that phones and computers use, so a change to or from summer time is followed on the right date. The difference from your time is worked out again every second, so it changes on the day the clocks change.
Q26: Why does my time zone say Kolkata and not Calcutta?
A26: India's time zone is called Asia/Kolkata in the tz database. Some browsers still give the older name, Asia/Calcutta, and the same goes for a few others such as Kyiv (Kiev), Ho Chi Minh City (Saigon) and Yangon (Rangoon). The page shows the current names.
Q27: What do the sun and the moon on a card mean?
A27: The sun shows daytime hours there, from 6 in the morning to 6 in the evening, and the moon the hours from 6 in the evening to 6 in the morning. They are a quick guide to whether it is a sensible time to call, not the real sunrise and sunset; the site's Sun and Moon tool gives those for any place.
Q28: How is this different from the Time Zone Converter and the Epoch Converter?
A28: The Time Zone Converter converts a time you type between zones and plans meetings across them; the World tab here shows the time now in the cities you pick, next to your alarms and timers. The Epoch Converter counts down to a date and turns timestamps into dates; the Timer here is a kitchen-style countdown of hours, minutes and seconds that rings when it reaches zero.
5. Settings, Data and Keys
Q29: What are the clock faces?
A29: Six looks for the analogue clock: Classic (every minute mark and the numbers), Numbers (the hour marks and the numbers), Marks only, Minimal (only the hour marks), Bold (thick hands) and Accent (the hands and face in the site's purple). Choose one under Clock face on the Clock tab.
Q30: How do I make the clock full screen?
A30: Press Full screen on the Clock tab, or F. The time fills the screen with the date under it, in the site's light or dark theme. Move the mouse or tap to see the Exit full screen button; Esc or F closes it.
Q31: What are the keyboard shortcuts?
A31: While you use the tool and are not typing: 1 to 5 switch between the tabs, Space starts and pauses the timer or the stopwatch, L adds a lap, R resets the timer or the stopwatch, F opens the full screen clock on the Clock tab, and Esc dismisses an alarm or closes a window. Elsewhere on the page these keys do what they always do.
Q32: How do notifications work?
A32: Turn on Show a notification in Sound and settings and allow notifications when your browser asks. A message then appears when an alarm or the timer rings while you are in another tab or window. It is shown by your own browser and system while this page is open; nothing is sent from a server.
Q33: Can I change the sounds or the volume?
A33: Each alarm has its own sound: Chime, Beep, Bell, Digital or Soft, made in your browser. Sound and settings sets the volume (with Test) and the sound for new alarms and the timer.
Q34: Where are my alarms kept, and how do I move them?
A34: In this browser on this device. Nothing is saved on a first visit until you change something. Save a backup in Sound and settings to get one small file with your alarms, cities and settings; Restore a backup reads it back, in this browser or another, after asking before it replaces anything. Restored alarms count from the moment they are restored, so a time already past does not ring.
Q35: How do I delete everything?
A35: Delete everything, under Sound and settings, removes all alarms, cities and settings this tool keeps in this browser, and stops the timer and the stopwatch, after you confirm; the rest of the site is left alone. A single alarm or city can be removed on its own, with Undo in the message.
Still have a question?
The help page walks through every part of Clock. For anything else, use the contact form.