In the early morning of February 14, 2025, Android cell phones in São Paulo, Rio de Janeiro, and Minas Gerais rang simultaneously with a warning of an earthquake of up to 5.5 magnitude on the coast of São Paulo. Many people woke up startled. The earthquake did not occur—the National Observatory and the seismology center of USP (University of São Paulo) recorded nothing.
Google deactivated the system in Brazil, investigated, adjusted the detection criteria, and reactivated the feature in April of that year. It is working today, with stricter filters against false positives.
This story sums it up well: the alert on your cell phone is real, it's useful, it's free — and it has limits that you need to know so you don't trust it too much or too little. This guide shows the three alert levels available in Brazil, how to activate each one, and what to do in the seconds the alert appears.
The three alert levels that exist in Brazil
They are independent systems, with different technologies and scopes. Ideally, you should have all three, because each one covers a shortcoming of the other:
- Android Earthquake Alert System — Detects tremors using an accelerometer and alerts you in seconds. Native, no installation required.
- Civil Defense via SMS (40199) — Disaster risk warning via text message. Requires registration, works on any mobile phone.
- Civil Defense Alert — Antenna transmission to all devices in a region. It does not require registration, but it does not yet cover the entire country.
How Android detects earthquakes without a seismograph.
The idea behind the system is ingenious: almost every smartphone has an accelerometer, the same sensor that rotates the screen when you lay the device down. It's sensitive enough to detect vibration.
A cell phone alone is useless — it vibrates when it falls on the sofa. But when Many devices in the same region register vibration at the same instant., With the characteristic signature of an earthquake, the pattern ceases to be noise and becomes data. Google has transformed the Android installed base into the world's largest seismic detection network, without installing a single sensor.
Physics provides the basis: an earthquake emits two main waves. P wave It arrives first and is weak. A S wave It arrives later and is the one that knocks things down. Because internet signals travel faster than seismic waves, detecting the P-wave near the epicenter allows those further away to be warned via network—before the S-wave arrives.
That's where the warning window comes from: normally seconds, Sometimes a few tens of seconds. It's not a minute and it's not an hour.
What changed after the false alarm?
The February 2025 incident was caused by activity in the sea near the coast of São Paulo combined with a calibration that was not adequate for the Brazilian reality. The system interpreted the combination as a tremor and triggered the alarm.
After suspending the feature, Google strengthened its analysis of unusual patterns and restricted detection criteria before reactivating it. The practical result is a more conservative system: less chance of false alarms, and also less chance of triggering a border event.
How to activate earthquake alerts on Android
- Open Settings.
- Go to Safety and emergency (on some devices, Google → Emergency alerts).
- Tap on Earthquake alerts.
- Activate the key.
Also check, on the same screen, if the wireless emergency alerts They are connected — this is the channel through which the Civil Defense warning is transmitted via antenna. It is advisable to keep the extreme and severe risk warnings activated.
Two details are important. The feature consumes virtually no battery power because detection occurs primarily when the device is stationary and charging. And it depends on a connection to receive the notification, even though the detection is local.
Civil Defense via SMS: thirty-second registration
For the average Brazilian, this is the most useful of the three layers — because the risk that kills the most people here isn't earthquakes, it's water and mud.
The procedure is free and takes less than a minute:
- Open the messaging app on your phone.
- Send an SMS to the number 40199.
- In the body of the message, write only the postal code which one you want to monitor, without periods or dashes.
- Please wait for registration confirmation.
From then on, you'll receive alerts when Civil Defense identifies a disaster risk in that region—storm, flood, or landslide. You can register more than one zip code: your home zip code, your work zip code, and the zip codes of family members you want to monitor.
The great advantage of SMS is precisely that it's old-fashioned. It doesn't need internet, it doesn't need a smartphone, and it arrives on a simple device — which is exactly what matters when the data network and power go down.
Civil Defense Alert: the warning that arrives unsolicited.
The latest technology is called Cell broadcast, or cellular transmission. Instead of sending a message to a list of registered users, the system activates the operators to send the notification to all cell phones connected to the antennas in that region.
This solves two problems at once: no one needs to be registered, and those passing through the area are also notified — tourists, truck drivers, those visiting relatives.
The honest caveat is coverage: the system is being gradually implemented and does not yet reach the entire national territory. Therefore, it complements, but does not replace, registration via SMS.
Apps: Which ones work in Brazil and which ones don't?
This is where most lists in Portuguese go terribly wrong, recommending a service to Brazilian readers that only works in the United States.
LastQuake, The recommendation from EMSC is the one that holds up. EMSC is a non-profit scientific organization founded in 1975, based in France, that gathers data from seismological observatories of dozens of institutes in dozens of countries. The app shows confirmed events within the first few minutes and has an interesting feature: anyone can report that they felt the tremor, which creates a collaborative map of where the tremor was felt. It works globally, which includes Brazil.
MyShake, The app from the University of California, Berkeley, is a serious and well-built app — but the His advance warning only covers California, Oregon, and Washington., This is because it depends on the ShakeAlert system from the US Geological Survey. In Brazil, it serves as an event viewer, not as an early warning system. It's worth installing knowing this; it's not worth installing thinking you'll receive advance alerts here.
For officially sourced weather information, the channels of Brazilian monitoring agencies and your state's Civil Defense are the most reliable source, and many maintain profiles and websites with updated bulletins.
No app can predict earthquakes.
This needs to be said explicitly, because the app store is full of things that suggest otherwise.
Nowhere in the world is there a technology capable of predicting an earthquake—of saying that it will happen in a certain place, on a certain day, with a certain magnitude. What science does is... to estimate risk on a scale of decades for a region and detect the tremor in the first few seconds after he started.
Any app that promises predictive status is lying, and the model is usually the same: subscription, aggressive advertising, or data collection. Early warning and prediction are different things, and the confusion between the two is what sustains this type of app.
What to do in the seconds of the alert.
Receiving the warning and staring at the screen is pointless. Time is short and the objective is modest: to avoid being hit by something falling.
- If you are indoors: Protect your head and neck, stay away from windows, mirrors, and high shelves, and crouch under a sturdy piece of furniture. Do not run outside during the tremor.
- If you are on the street: Stay away from building facades, poles, and power lines.
- If you are driving: Slow down, stop in an open area, and remain in the vehicle.
- In case of flood or landslide warning: Leave the low-lying area or the slope immediately. Don't wait to see the water rise. This is the only case where leaving early is always the right decision.
It's a good idea to agree on a meeting point with family and have a contact person from outside the city — in an emergency, local calls get congested before long-distance calls.
Frequently Asked Questions
Does earthquake alert work on iPhone?
The system described here is from Android and uses devices with that operating system. On iPhones, official warnings arrive via government emergency alerts, which should be kept enabled in notification settings.
How much notice will I receive?
Seconds, in most cases. The farther you are from the epicenter, the larger the window. Those who are directly over the epicenter may feel the tremor before any warning arrives.
Do I need internet to receive it?
For the Android alert, yes. For the Civil Defense SMS, no — and that's why it's worth having both.
I registered my zip code and I'm not receiving anything. Is it working?
Probably yes. The alert is only triggered when a risk has been identified for that area. Silence, in this case, is good news.
Could the Android system make another mistake?
It's possible. No automatic detection system is infallible, and Google itself treated the 2025 episode as a learning experience, tightening its criteria. An occasional false alarm is the price of a system that warns in seconds.
Is it worth activating even if you live far from a high-risk area?
It's worth it because it costs nothing and because the same configuration covers heavy rain and flooding — which happen in almost every part of the country. Plus, you get to travel.
Ten minutes, once in a lifetime.
In summary: turn on the earthquake alert system, confirm wireless emergency alerts, send an SMS with your home zip code to 40199, repeat the process for your work zip code, and, if you wish, install LastQuake. That's it.
None of these layers predict the future, and none replaces getting off a slope when the rain won't stop. What they do is give you information a few seconds or a few minutes before someone who hasn't configured anything—and, in a disaster, that difference is the only thing that's under your control.
