Guide
How ETA works
What happens from the moment you set a destination to the moment the alert goes off — and what stays on your phone.
1. You set a destination
Type a postcode or a town, or tap the map. Postcode and place search uses postcodes.io, a free UK lookup service: your search text goes to our server, which asks postcodes.io and passes the answer back. We don’t keep the search. Northern Ireland postcodes can’t be looked up (the data needs a separate licence for a site like ours), but you can tap the map anywhere.
The destination itself is kept in your browser. You can save places you use often (“Home”, “Work station”) — they’re stored on that phone only.
2. You choose when to be alerted
- A distance — 300 m up to 10 km, measured in a straight line from where you are to the destination.
- A number of minutes — 2 to 30. ETA works this out from how quickly you’ve been getting closer over the last three minutes or so. It doesn’t know about roads, timetables or traffic. If you’re within 300 m it counts as reached anyway, so a final slow crawl into a station still sets it off.
3a. Wake me / get off
When you reach the point you chose, ETA shows a screen-filling alert, plays a repeating chime and — on phones and browsers that support it — vibrates, until you press “I’m awake”. None of this involves our server. Browsers only let a page play sound after you’ve tapped something on it, so pressing Start (or “Test the alarm”) is what makes the sound possible later.
Vibration isn’t available everywhere. According to MDN’s browser compatibility data, Safari (on iPhone and Mac) doesn’t support the web Vibration API, and Firefox for Android has disabled it since version 79. Chrome on Android supports it after you’ve interacted with the page.
Source: MDN — navigator.vibrate() compatibility. Checked 20 October 2026.
Why the alert is an overlay, not “real” full screen. MDN’s data says the Fullscreen API is only available on iPad, not iPhone, so ETA covers the page itself instead.
Source: MDN — requestFullscreen() compatibility. Checked 20 October 2026.
3b. Tell my people
This needs a free account (your email address and a one-time sign-in link — no password), because ETA sends the emails for you.
- Add your people. Each person gets one invitation email with your name and email address. They only get alerts after they press “Yes”. They can say no, or ask ETA never to email them again.
- Start a journey and tick who to tell. You can give the destination a nickname such as “home” — that’s the only thing about the destination that reaches us.
- Nearly there: when you reach the point you chose, your phone tells our server “send the alert now”, with its estimate of the minutes left. We email your chosen contacts.
- Arrived: press “I’ve arrived”, or let ETA send it when you get within about 150 m.
The optional live ETA link
If you switch it on, the emails include a link to a page showing your latest position and estimate. To make that work, your phone sends your position to our server roughly every 30 seconds while the journey runs. We keep only the latest one, delete it when the journey ends, and end every journey after 24 hours at most (you can choose 1, 2, 4, 8 or 24 hours). Anyone with the link can open it until then, so only use it with people you trust.
4. Keep the screen open
This is the big limitation of a web app. Browsers only give location updates to a page that’s visible, so if you lock your phone or switch to another app, ETA can’t follow you and won’t alert anyone. ETA asks your phone to keep the screen on while a journey is running. Read why the screen has to stay open for the details.
What ETA can’t do (yet)
- Work in the background with the screen off — that would need a native app for iPhone and Android.
- Send texts or WhatsApp messages — emails only.
- Know about routes, delays or timetables — the estimate is based on straight-line distance and your recent speed.
Browser facts on this page checked against MDN and the W3C Geolocation specification on 20 October 2026.