Random Timer

How to use the random timer

1. This random timer generator runs online, in your browser. Type a Min and a Max, such as 30 and 3m, or tap a range like 30 s–3 min.
2. Press Start or the spacebar. A secret length between Min and Max is picked at that moment.
3. The display shows ?:?? while the countdown runs, so nobody knows the end.
4. At the secret moment a buzzer sounds and the page shows “It ran for 2:17.3”.
5. Press Start again for a new secret length, or Reset to change the range.

Games and drills that need a surprise end

• Hot-potato-style passing games. Pass a phone or a ball around the circle while the timer runs; whoever holds it at the buzzer is out. A range of 30 seconds to 3 minutes keeps everyone guessing.
• Word-guessing games. Describe words for your team and pass the phone on after each one. With 1 to 5 minutes nobody can pace themselves to the end.
• A visible fuse instead. If you’d rather see the time drain away, use the bomb timer.
• Reaction starts. Set 3 to 10 seconds and sprint, catch or answer at the buzzer.
• Workouts with unpredictable work periods. Turn on Repeat and every round gets its own length.
• Party lights. Pair the game with the disco light on a second screen.

How the random time is chosen (and why it’s fair)

The length is drawn the moment you press Start, before anything appears on screen, by your browser’s cryptographic random generator (crypto.getRandomValues). It picks a whole tenth of a second, and every tenth in your range is equally likely. For 0:30 to 3:00 that means 1,501 possible ends, an average of 1:45, and an end before 1:00 about one time in five.

The generator returns a number between 0 and about 4.3 billion. To turn it into one of 1,501 ends without favoring any of them, the page throws away the few numbers at the very top that don’t divide evenly, 1,393 of the 4.3 billion, and draws again. With Repeat on, every round is drawn at Start, each independently. The drawn times are stored in this browser, so a reload can’t pick a new one. One honest limit: someone with the browser’s developer tools could read the stored time. This is a game timer, not a security device.

Show or hide the time

By default everything that could give the end away stays hidden: the digits, the progress bar, the tab title and tab icon, the “Ends at” time and the spoken updates for screen readers. Press H or switch off Hide time while running to show it all; that suits workouts, where seeing the time left helps. Press H again to hide it, and the surprise comes back for the rest of the round.

Repeat rounds with a new time each

Need a timer that goes off at random times, again and again? Choose 2 to 99 rounds under Repeat. Each round gets its own secret length between your Min and Max. The end of a round plays one short buzz and “Round 2 of 5” appears; the full buzzer plays only after the last round. There is no break between rounds, so if you need a rest, set Min to your shortest rest.

Options explained

• Sound: Buzzer, which suits a noisy room. Pick any other sound, or Off, and press Test sound to hear it.
• Ring for: 10 s. Once, 30 s, 1 min or until you stop it are the others.
• Flash at zero: on. The colors invert once a second for ten seconds, never red, then a red border stays.
• Notify me when time is up: off. When on, a background tab shows a notification with the length it ran.

Tips and limits

• Keep the page open. Browsers slow hidden tabs; Chrome checks their timers about once a second, and after five hidden minutes only once a minute (Chrome’s timer throttling). That’s why every buzzer is booked on the audio clock at Start.
• Phones may pause pages in the background or when the screen locks.
• Tap or click the page once before the game, so the buzzer is allowed to play.
• On iPhone the timer fills the browser window rather than the whole screen; add the page to your Home Screen for more room.
• A laptop that sleeps through the end can’t buzz. When it wakes, the page shows how long ago time ran out, and how long the timer ran.

Updated November 6, 2026