This story was originally published on HackerNoon at: https://hackernoon.com/how-i-built-an-iphone-theft-detection-system-using-motion-sensors-and-screen-time-apis.
How I built phone snatch detection for iOS using accelerometer, Screen Time API, and a background location hack. No ML, no hardware.
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Android shipped Theft Detection Lock in 2024. Apple still has nothing. I built a free iOS app that detects phone grabs via accelerometer and locks selected apps using Screen Time shields. The technical rabbit holes: CMMotionActivityManager turned out useless (reports "Unknown" instead of "Running"), background execution requires a location manager hack to keep the process alive, Screen Time API has two token types you need to apply simultaneously, and Face ID can't be called from shield extensions. The app works but has one structural weakness – deleting it removes the shields.