How it works

Magnitude is building a volunteer network that relays earthquake warnings from Android phones to iPhones, starting in Colombia. This page explains how it works, what the different warning levels mean, which ones can wake you, where we are taking it, and how we test it.

Where a warning comes from

Google's Android Earthquake Alerts System uses the motion sensors in Android phones to detect earthquakes, estimates the magnitude and the epicentre within seconds, and alerts Android phones where shaking is expected. It does this for earthquakes of an estimated magnitude 4.5 or more. There is no public feed of these alerts, and iPhones in Colombia receive nothing like them.

Magnitude closes part of that gap with volunteers. A volunteer keeps an Android phone running our Quake Proxy app. When Google alerts that phone, Quake Proxy reads the alert off the screen and sends it to our server with the phone's approximate location. Our server then sends a warning to every iPhone whose chosen place is near enough to that phone.

The design is many volunteer phones spread across a region, so that wherever your place is, one is close enough to matter. Today the network is one volunteer phone, in Risaralda. A warning can reach you only when Google alerted a volunteer phone near your place, so coverage is narrow while the network is small. Volunteers are how it grows.

Magnitude and intensity

Magnitude describes the earthquake itself: one number for the whole event. Intensity describes the shaking at a particular place, and it falls with distance. The same earthquake can be violent near the epicentre and barely felt 200 km away.

Intensity is measured on the Modified Mercalli Intensity scale, written in Roman numerals. Google's alert levels are defined by the intensity expected where the phone is, not by magnitude.

Google's three alert levels

Google sends each Android phone one of three alerts, depending on the intensity it expects at that phone's location:

Each level covers an area around the estimated epicentre, sized by the estimated magnitude and depth. In Google's published examples, an earthquake of magnitude 5.5 at 20 km depth sends Take Action up to about 8 km away and Be Aware up to about 197 km; at magnitude 6.5 those distances grow to 78 and 442 km. Google does not publish how far Be Ready reaches. Read Google's description of the alerts.

Most people who receive an alert are far from the epicentre, so most alerts are Be Aware. Be Aware still means shaking can be felt: intensity IV wakes some people.

What Magnitude sends you

We see only the alert Google gave the volunteer phone, at the volunteer phone's location. So Magnitude's warning depends on two things: which alert the volunteer phone received, and how far your chosen place is from that phone.

Act now and Get ready open a full red screen with three instructions: drop, cover, hold on. Heads up opens an amber screen you can dismiss at once. Beyond 200 km you receive nothing.

The distances allow for the uncertainty in both locations, and that allowance only ever widens the circle. They are our relay policy, not a calculation of the shaking at your place: a warning from Magnitude says what was observed and how far from your place, never that Google predicted a given intensity for you.

The distances are deliberately generous because the network is sparse: with one phone, a single observation has to stand in for a wide area. As more volunteer phones join, the plan is for the nearest phones to decide what you receive, so the circles can tighten toward what Google actually sent near your place.

What can wake you

An iPhone that is silenced or in a Focus stays quiet for ordinary notifications. Only a Critical Alert sounds anyway. To get them, allow Critical Alerts when the app asks, and keep Critical Alerts on in the app's Settings. From version 1.1 you then choose which kinds may sound:

The defaults follow Android: it sounds an alarm for Take Action and Be Ready, and only a notification for Be Aware. If you would rather be woken for anything Google flags within 200 km of your place, turn on Light shaking alerts. The cost is being woken now and then for shaking you might have slept through. Test alerts never sound when your phone is silenced, whatever you choose.

One earthquake, one notification

Google often revises an alert within seconds as its estimate improves, and posts an update after the shaking. Magnitude treats everything one volunteer phone sees within five minutes as one earthquake. A revision reaches you only if it raises your warning, for example from Heads up to Get ready, and then it replaces the earlier notification rather than adding another. Google's after-the-fact update ("Earthquake at 4:13 AM · You may have felt shaking") is kept on our server and never sent as a warning.

A warning that cannot be delivered within a minute of the alert is dropped rather than shown late.

What it cannot promise

Magnitude is a supplement to official warnings, never a warning system. Every step depends on phones, networks and services that can be slow or fail: Google has to detect the earthquake and alert a volunteer phone near your place, that phone has to be on and online, and our server and Apple's push service have to deliver in time. Close to the epicentre, the shaking can arrive before any warning. If you feel shaking, protect yourself first.

Where we are going

Magnitude is new, and what this page describes is the start of a larger design. These are the next steps we are working on. They are plans, not promises, and this page will change as they ship.

More volunteer phones

A volunteer app, Magnitude Proxy, that anyone with a suitable Android phone can set up from this website, so the network can grow well beyond our own test phone.

Warnings from the nearest phones

When several volunteer phones observe the same earthquake, each person's warning will come from the phones closest to their place. A later, nearer or stronger observation upgrades a warning already on its way; nothing downgrades or withdraws a warning while the earthquake is happening.

Magnitude for Android

A Magnitude app on Google Play for recent earthquakes and earthquake notifications. Android phones already receive Google's warnings directly, so the Android app does not relay them.

Measuring every warning

Google's alerts carry their own estimate of the magnitude, the distance and the moment the earthquake began. We now keep those with every warning, so each one can be compared with the official report from SGC and we can learn how much notice the network really gives.

How we test it

Magnitude is new, and real earthquakes are its hardest test. At 4:13 a.m. on 3 November 2026 a magnitude 5.6 earthquake near Chaparral, Tolima, was felt across central Colombia. Our volunteer phone, about 112 km away, received Google's Be Aware alert and, a second later, Be Ready. Our server relayed the first to iPhones 16 seconds after the earthquake began, by our estimate about 15 seconds before the strongest shaking reached the area around the phone.

It also showed us a gap. On Android, Be Ready sounded an alarm and woke people. Magnitude knew only two levels, so iPhones near the phone received an ordinary notification, which is easy to sleep through at 4 a.m. Later that day we taught the relay Google's three levels, added the Critical Alert choices above, and stopped sending Google's after-the-fact update as a new warning.

Before a change like that reaches anyone, automated tests replay that morning's alerts word for word and check what each person would receive. Then we test on real devices: Google's own demos run end to end through the volunteer phone, marked as tests so they never reach anyone as a real warning, and a Critical Alert is sent to an iPhone on silent to confirm that it sounds.