What is an accident-detection safety app and how does it work?
An accident-detection safety app uses your phone's or watch's motion sensors to spot a likely crash or hard fall, then asks if you're OK. If you don't respond before a countdown ends, it alerts someone: emergency services, your chosen contacts, or both, depending on the product. Apple's Crash Detection and Fall Detection can call emergency services; Garmin incident detection messages your contacts. Holler offers an opt-in crash detection beta that alerts your Guardians, not 911.
How accident detection works
01Sensors watch for an impact pattern
The accelerometer and gyroscope look for a sharp spike in force followed by stillness. Some systems add GPS speed or other signals. Apple, for example, describes its Crash Detection as designed for severe car crashes, while Fall Detection on Apple Watch looks for hard falls.
02A check comes before any alert
A detection doesn't alert anyone straight away. The device taps, sounds or shows an "Are you OK?" prompt so you can cancel. Apple Watch waits if it senses you moving, and starts a 30 second countdown only after about a minute of stillness.
03An unanswered countdown sends the alert
What happens next depends on the product. Apple's features call emergency services and message your emergency contacts with your location. Garmin's Edge manual says incident detection sends your contacts a text and email with your location after 30 seconds, and that the Garmin Connect app does not contact emergency services for you.
04Expect misses and false alarms
Every system trades one against the other. A dropped phone or a hard landing can look like a crash, and a slow slide, a medical collapse or a fall where you keep moving may not register. Apple says its watch cannot detect all falls. Treat detection as one layer, not the plan.
05Where Holler fits
Holler's crash detection is an opt-in beta: a possible hard fall or crash followed by stillness starts an "Are you OK?" countdown, and your Guardians are alerted with your live link if you don't respond. In a browser it only works while the page is open and the screen is on. It can miss real crashes and can false-alarm, and it never calls 911.
Related questions
Will an accident-detection app call 911 for me?
Only some will. Apple Watch Fall Detection and iPhone Crash Detection can call emergency services on supported devices. Garmin incident detection and Holler alert the contacts you choose, who then decide whether to call 911. Know which kind you're relying on before you head out.
What if I'm hurt but not in a crash?
Impact detection won't help with a sprained ankle, heat illness or a slow collapse. That's where a stationary alert or a return time helps. Holler's optional stationary alert asks "Are you OK?" if you stop moving for the time you choose, and a missed return time sends your Guardians an overdue alert.
Does accident detection work without cell service?
The sensors can still notice an impact, but the alert needs a way out. Apple says Fall Detection can use cellular, Wi-Fi calling or, on supported models, a satellite connection. Garmin needs your paired phone to have data coverage. A live location link stops updating without signal.
Which option is best for cyclists?
It depends on your gear. A Garmin bike computer or an Apple Watch adds well-tested detection, and a live link tells people at home where you are. Our guide to crash detection options for cyclists compares them.
More safety questions
Compare your options
Sources, checked September 2026: Apple Support: Use Crash Detection on iPhone or Apple Watch, Apple Support: Use Fall Detection with Apple Watch, Garmin Edge 840 Owner's Manual: Incident detection.
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