How to use the online alarm clock
Hand over the remaining preparations now, then use the 8:21 am alarm to mark when responsibility for reaching Heathrow passes to the next person. That gives them a clear cue to gather the travel documents, check the departure details and leave enough room for security before an early flight. With 9:00 am approaching, the alarm separates the handover from the final stretch towards the terminal.
A quiet tone suits a handover made beside sleeping family or in a hotel room, while a more insistent sound is safer if the traveller may be packing, showering or moving luggage. Set the volume and tone for where the alarm will actually be heard, then keep the browser running. If the page is closed or the phone falls asleep, the alarm may stay silent and the Heathrow security check could be missed.
For an early Heathrow departure, base the leaving time on the route at 8:21 am rather than a late-night estimate. Morning traffic can build quickly on the M4, M25 and airport approaches, while Underground or Elizabeth line journeys still need time for walking, platform changes and the terminal transfer. Add a small buffer before the planned handover so a delayed connection does not consume the time reserved for security.
Common questions
Do I need an account or an app?
Neither. Choose a time and a sound, press Start, and it runs in this browser tab. Nothing is downloaded, nothing is registered, and closing the page leaves nothing behind on the device.
Can I change the sound?
Yes, there is a short list of tones to pick from before you press Start. Softer sounds are easy to sleep through, so a firmer bell tends to be the safer choice for anything early in the morning.
Will it still be right when the clocks change?
Yes. It reads your device's local clock, so the move between GMT and BST at the end of March and October is picked up automatically, as long as the computer's date, time and time zone are set correctly.
Can I use this on a phone?
It works in a mobile browser, but phones lock the screen and suspend background tabs far more readily than a laptop does, which can stop the alarm sounding. For anything important, a desktop or a plugged-in laptop is the steadier option.
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