Automatic crash notification and SOS: how your car calls for help and how to check it

Learn whether your car’s emergency call system is active and how to keep it working

Safety Behind the Wheel Foundationdrivewithcare.org

Last reviewed:

For every driver17 min read

Roadside emergenciesVehicle safety systemsEmergency careTelematics and driver monitoringCrash scene steps

Safety Behind the Wheel Foundation built this guide from National Highway Traffic Safety Administration (NHTSA) research and guidance, Federal Communications Commission (FCC) notices, the European Commission’s European Road Safety Observatory and published studies in trauma and emergency medicine journals. Every source is listed at the end.

When the car has to make the call

Most collisions are reported by someone with a phone. But some wrecks happen at night, on empty roads, or to a driver who is alone and knocked out. Then the first call for help may come late or not at all.

That delay can matter. In 2021, 42,939 people died in traffic collisions in the United States [1]. Four in 10 of them were still alive when first responders reached them [1]. Faster notice will not save everyone, but it gives emergency care more time to work.

Automatic crash notification, often shortened to ACN, is a vehicle system that senses a serious collision and sends an alert without anyone touching a button. These systems, sometimes called mayday systems, can reach emergency help within seconds [2]. Most also have an SOS button you can press yourself.

A more advanced version, called advanced automatic crash notification (AACN), also sends details of the impact that help predict how badly people inside may be hurt. The alert may go straight to a 911 center or pass through a private call center first [3].

This guide covers the equipment: how it works, whether yours is active, and how to keep it ready. For what to do at the scene, see our guide to post crash care.

Think of the system as a chain. Telematics means a vehicle’s built in computer and cell connection working together. Every link has to hold for the alert to reach help.

  1. Sensing. The car decides a serious collision has happened. Most systems are set off when an air bag deploys, though other crash sensors can be used [2].
  2. Locating. A satellite receiver finds the vehicle’s position.
  3. Connecting. A cell module built into the car places a call and sends data. It needs power, an antenna and a network it can still use.
  4. Answering. Some systems connect straight to a 911 center. Others reach a private call center first, where an operator tries to talk with the people inside and then hands the case to 911 [3, 5]. A federal notice describes U.S. telematics services that pair crash notification with navigation, concierge and diagnostic features, run through these call centers [4].
  5. Responding. Dispatchers send police, fire and EMS crews, ideally with the location and impact details in hand.

Europe’s version, called eCall, shows what a complete unit looks like. It must include a satellite receiver, a cell antenna, a crash sensor, a hands free speaker and microphone, a backup power supply, a manual call button and a status light [5]. Systems elsewhere often use similar parts, but features vary by maker and model.

What the alert can carry

Basic systems send the location and vehicle details. Some add the type of collision and how severe it was [2]. Injury prediction research uses delta V, the sudden change in the vehicle’s speed during the impact, plus the direction of the hit, seat belt use and the number of impacts [7].

Europe’s eCall sends a small, fixed set of facts. It covers the time, location and direction of travel, the vehicle ID number, and whether someone pressed the button or the car called on its own [5]. It also lists the fuel or power type, such as electric or hybrid [5]. That can help crews prepare before they arrive.

Where the chain can slow down

Each handoff adds time. In one German city in 2023, automatic alerts relayed by service centers took about a minute longer to dispatch than other accident calls [5]. The averages were 2 minutes 41 seconds versus 1 minute 39 seconds [5]. Those calls came in on a line without priority status, and the authors noted that map positions may need to be turned into street addresses [5]. In the United States, trauma surgeons note that crash data from vehicles is still hard to pass directly to 911 centers [6].

What the research says about speed and survival

Studies point the same way: earlier notice tends to mean earlier care.

Comparison compiled by Safety Behind the Wheel Foundation

Research on automatic notification and emergency response

FindingSettingSource
Median time to notify EMS: 2 minutes with an ACN vehicle involved, 4 withoutU.S. crash sample, 2017[9]
Median time to reach a hospital in less urban areas: 36 minutes with ACN vs. 45 withoutU.S. crash sample, 2017[9]
Estimated 360 to 721 lives saved a year with full AACN useU.S. fatal crash data, 2009 to 2015[3]
Estimated 2 to 4 percent fewer road deathsEuropean review, 2023[11]

Rural collisions show why minutes count. When notice took more than 30 minutes, rural crashes were more likely to be fatal than urban ones with similar delays [10]. Freeing trapped people also stretched the time before hospital care, and crash data could tell crews early when to bring rescue tools [10]. See our guide to rural road safety for more on rural response times.

Crash data can also help send patients to the right hospital. In a small Michigan field study, a crash data model flagged about 73 percent of occupants with serious injuries [7]. The field rules used at the time caught 56 to 66 percent [7]. The national guideline EMS crews use to pick a hospital lists vehicle crash data that points to severe injury as a reason to consider a trauma center [8]. It also notes that research on using this data in real time is still lacking [8].

Keep the big estimates in context. They assume every vehicle has the system and every road has cell coverage [3]. In 2017, only about 9 percent of collisions in a national sample involved at least one vehicle with ACN [9].

Your options: built in, add on and personal alerts

Automatic alert tools fall into a few groups, all with one job: start help when you may not be able to ask.

Comparison compiled by Safety Behind the Wheel Foundation

Emergency alert options and what each depends on

OptionHow it is set offWhat it depends on
Built in crash notificationAir bag deployment or crash sensorsActive service, cell module, network, vehicle power
Built in SOS buttonSomeone presses itSame as above, plus a person able to reach it
Add on crash alert deviceSensors inside the device, often with a buttonDevice plan or phone app, secure mounting, power
Phone or watch crash detectionMotion sensors in the deviceFeature turned on, charged device, signal

Who uses them. They matter most for people who often drive alone, at night or on rural roads. Researchers have suggested older adults may gain the most, because they are more likely to be badly hurt [2]. Parents of new drivers and employers with solo work drivers should check too. In Europe, expansion to trucks and motorcycles is planned [5].

Where to get them. Built in systems come from the factory and are activated through the dealer or the automaker’s app. Add on devices are sold by electronics stores, auto parts stores and wireless carriers. Phone and watch crash detection lives in the device settings. A companion guide covers setup.

How to choose an add on. Ask these questions before you buy:

  • Does it work with your vehicle and phone?
  • Does its cell network cover the roads you drive?
  • Who answers: a 911 center, a call center or only your contacts?
  • Is there a countdown you can cancel to stop false alerts?
  • What does the plan cost, and what happens when it ends?
  • How is your location data stored and shared?

Does your vehicle have it, and is it switched on?

Do not assume your car has ACN. These systems are not standard on every U.S. vehicle [6]. Europe, by contrast, has required eCall in new models of passenger cars and light commercial vehicles since 2018 [11].

Use this routine to find out where you stand:

  1. Look for buttons labeled SOS, emergency or assist, often near the rearview mirror or in the overhead console.
  2. Search the owner’s manual or the automaker’s app for terms like “emergency call,” “crash response” or “SOS.”
  3. Check the status light, if there is one. Your manual explains what each color means.
  4. Call the dealer or service provider with your vehicle identification number (VIN). Ask them to confirm the service is active.
  5. Ask whether the automatic alert needs a paid plan. Ask when any free period ends and whether you will be warned first.
  6. If the plan lapses, ask whether the automatic alert stops, the SOS button stops, or only extra features stop.

With a used car, the service may still be linked to the last owner and their contacts. Close that account and open your own.

Network shutdowns and dead zones

An automatic alert is only as good as the network it rides on. Cell companies retire older network types to make room for newer ones. Major U.S. mobile providers finished shutting down their 3G networks in 2022 [12].

A cell module built only for a retired network cannot place a call, even if the button still lights up. Ask the automaker or dealer whether your module was affected and whether an upgrade is offered. Act on any notice about future network changes.

Coverage is the other gap. Estimates of lives saved assume cell service everywhere [3], but canyons, mountains and remote highways still have dead zones. In those places, an alert may fail or wait until the car can connect.

So keep a charged phone and a charger in the car. NHTSA’s winter kit list includes both, along with first aid supplies, blankets, a flashlight, water and food [13]. If you are stranded in winter, NHTSA advises staying with your car, making it easy to see and keeping the exhaust pipe clear of snow [13]. Safety Behind the Wheel Foundation gives drivers the same advice. Our roadside breakdown guide covers staying safe while you wait.

Keep contacts and account details current

A call center can only reach the people and numbers on file. Old details waste time when no one in the car can talk.

These services also share your location, so read the privacy settings. Before a car leaves your hands, follow our guide on what to do before your wrecked car leaves your hands to clear accounts and personal data.

Test it without setting off a false alarm

Accidental alerts are a real problem. A study of eCall alerts to Polish fire services from 2016 to 2022 found many false alarms and called for better user education [14]. Europe’s data set even includes a flag that marks a call as a test [5].

Here is a safe yearly check:

  1. Read the testing section of your manual. Some providers offer a test mode or a set test procedure.
  2. If your car has a nonemergency or information button, use it to reach the call center. Ask them to confirm your location, account status and contacts.
  3. Do not press SOS or call 911 just to test, unless the provider tells you to.
  4. During the call, make sure you can hear the operator and the operator can hear you.
  5. Repeat the check after any collision repair, battery replacement or major software update.

If you press SOS by mistake, do not hang up. Stay on the line and explain, so no one is sent out for nothing.

Limits and common mistakes

Automatic notification is a strong safety net, but it has holes.

  • Not every collision sets it off. Systems usually react to air bag deployment [2]. A low speed collision or one that does not deploy an air bag may not trigger an alert.
  • Damage can break the chain. A collision can cut power or crush an antenna. Ask whether your system has backup power, as eCall must [5].
  • No signal or no plan can mean no alert. Dead zones, retired networks and lapsed plans all stop the call.
  • Predictions are estimates. In EMS triage rules, crash data is one warning sign among many, not the final word [8].
  • Waiting on the car. If you can call 911 yourself, do it. If an operator speaks through the cabin speakers, answer.

Care after a collision, repair or sale

ACN parts sit in places that collisions and repairs disturb, such as the roof, mirror area and dashboard. Treat them like any other safety system.

Telling the shop matters. The Polish study suggested some mechanics did not know to turn off eCall before working on a car, a source of false alarms [14]. At pickup, add this system to our repaired car pickup checklist.

Frequently asked questions

Does automatic crash notification call 911 directly?

It depends on the system. Some connect straight to a 911 center. Others go first to a private call center, where an operator tries to talk with the people in the car and then contacts 911 [3, 5]. Either way, the goal is to start help without waiting for someone to dial. Ask your provider which way your system works.

Will my car’s SOS button work if my plan has ended?

Not always. What still works after a plan ends depends on the automaker and the plan. Do not guess. Call the dealer or provider with your VIN. Ask whether automatic crash alerts and the SOS button stay active, and whether you will be warned before anything shuts off. Get the answer in writing if you can.

My car is from before 2022. Could the 3G shutdown affect it?

It could. Major U.S. mobile providers finished shutting down their 3G networks in 2022 [12]. A module that could only use 3G cannot reach anyone now, even if the button lights up. Give the automaker or dealer your VIN and ask whether your module was affected and whether an upgrade exists.

Can I add crash notification to an older car?

Often, yes. Add on crash alert devices and phone or watch crash detection can fill the gap. Use the buying questions above: fit, network coverage, who answers, false alert controls and cost. Mount any device securely so it does not fly around in a collision.

Is phone crash detection a good substitute?

It is a useful backup, and for some older cars it is the main option. But a phone can be thrown, broken, left at home or dead. A built in system is wired to the car’s power and crash sensors. Using both, with contacts kept current in each, gives you two chances to get help.

The bottom line

Recommendation from Safety Behind the Wheel Foundation

Safety Behind the Wheel Foundation encourages every driver to confirm that the car’s emergency call system is active, connected and tied to current contacts. Automatic crash notification can turn a wreck no one sees into a call for help within seconds. It works only when every link holds: sensors, power, antenna, network, an active account and current contacts. Earlier notice can shorten the time to care, especially on rural roads [9, 10].

Take ten minutes this month. Confirm your car has the feature, the service is active and it still connects. Update your contacts, check it the safe way, and keep a charged phone as your backup.

Sources and further reading

  1. 1Goolsby C, Bosson N, Banjo E, et al. National research agenda for postcrash care. Journal of Trauma and Acute Care Surgery 98(6):942-950 (via PubMed). Published 2025. Data year: 2021. pubmed.ncbi.nlm.nih.gov/40152599
  2. 2Eby DW, Molnar LJ, Zhang L, et al., University of Michigan Transportation Research Institute. Use, perceptions, and benefits of automotive technologies among aging drivers. Injury Epidemiology 3:28 (via PubMed Central). Published 2016. pubmed.ncbi.nlm.nih.gov/27868168
  3. 3Lee E, Wu J, Kang T, Craig M, National Highway Traffic Safety Administration. Estimate of mortality reduction with implementation of advanced automatic collision notification. Traffic Injury Prevention 18(sup1):S24-S30 (via PubMed). Published 2017. Data year: 2009 to 2015 (FARS); 2000-2015 (NASS-CDS). pubmed.ncbi.nlm.nih.gov/28384071
  4. 4Federal Communications Commission, Federal Register. Facilitating the Deployment of Text to 911 and Other Next Generation 911 Applications; Framework for Next Generation 911 Deployment (proposed rule, document 2014-21852). Published September 16, 2014. federalregister.gov/…/facilitating-the-deployment-of-text-to…
  5. 5Brune B, Haut F, Wolf M, et al. Comparison of dispatching after motor vehicle accidents: effects of the TPS-eCall system on dispatching time. BMC Emergency Medicine 25:184 (via PubMed Central). Published 2025. Data year: 2023. pubmed.ncbi.nlm.nih.gov/40988067
  6. 6Chin TL, Valenzuela JY, Duncan T, et al. Advanced Automatic Crash Notification Systems: It Is Time to Adopt Potentially Life-Saving Technology. Journal of the American College of Surgeons (via PubMed). Published September 2026. pubmed.ncbi.nlm.nih.gov/42627114
  7. 7He K, Zhang P, Wang SC. Crash Telemetry-Based Injury Severity Prediction is Equivalent to or Out-Performs Field Protocols in Triage of Planar Vehicle Collisions. Prehospital and Disaster Medicine 34(4):356-362 (via PubMed). Published 2019. Data year: 1999 to 2013 (NASS-CDS); 2008-2011 (Michigan field data). pubmed.ncbi.nlm.nih.gov/31322099
  8. 8Newgard CD, Fischer PE, Gestring M, et al. National guideline for the field triage of injured patients: Recommendations of the National Expert Panel on Field Triage, 2021. Journal of Trauma and Acute Care Surgery 93(2):e49-e60 (via PubMed Central). Published 2022. pubmed.ncbi.nlm.nih.gov/35475939
  9. 9Griffin RL, Carroll S, Jansen JO. Automatic collision notification availability and emergency response times following vehicle collision: an analysis of the 2017 Crash Investigation Sampling System. Traffic Injury Prevention 21(sup1):S135-S139 (via PubMed). Published 2020. Data year: 2017. pubmed.ncbi.nlm.nih.gov/33040588
  10. 10Plevin RE, Kaufman R, Fraade-Blanar L, Bulger EM. Evaluating the Potential Benefits of Advanced Automatic Crash Notification. Prehospital and Disaster Medicine 32(2):156-164 (via PubMed). Published 2017. Data year: 1996 to 2012 (CIREN); 2000-2011 (FARS and NASS-CDS). pubmed.ncbi.nlm.nih.gov/28137341
  11. 11European Road Safety Observatory, European Commission. Road Safety Thematic Report: Post-impact care. Published 2023. Data year: various, up to 2021. road-safety.transport.ec.europa.eu/…/2976be95-90f3-4a5c-8045-d9893b5f75a2_e…
  12. 12Federal Communications Commission, Federal Register. Establishing the Digital Opportunity Data Collection; Modernizing the FCC Form 477 Data Program; Delete, Delete, Delete (proposed rule, 91 FR 37928, document 2026-12767). Published June 24, 2026. Data year: 2022 (3G shutdowns); 2025 (provider filings). federalregister.gov/…/establishing-the-digital-opportunity-d…
  13. 13National Highway Traffic Safety Administration. Winter Weather Driving Tips: Prepare Your Vehicle. Updated date not shown; reviewed October 2026. nhtsa.gov/winter-driving-tips
  14. 14Kubiak T, Dudziński Ł, Kasperczyk R, Czyżewski Ł. Emergency services response to eCall System alerts: Observations from 2016-2022 in the National Fire and Rescue System. Traffic Injury Prevention 25(6):819-824 (via PubMed). Published 2024. Data year: 2016 to 2022. pubmed.ncbi.nlm.nih.gov/38905156

This article reflects the safety priorities of emergency response and connected vehicle safety systems. It is general education, not legal, medical, insurance or financial advice. Features, plans and network support differ by automaker, model and provider and can change, so verify details with official sources. For your own vehicle, contact the dealer, the automaker or your service provider. In an emergency, call 911. Reviewed October 2026.

Cite this article: Safety Behind the Wheel Foundation. “Automatic crash notification and SOS: how your car calls for help and how to check it.” drivewithcare.org, https://drivewithcare.org/automatic-crash-notification-emergency-sos/. Reviewed October 2026.

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