# Automatic Drive Tracking (ADT)

> Apple's term for sensor-fusion-based drive detection. The technology that lets an iPhone log a business mile without you opening an app.

Category: mileage-and-vehicle-expenses
Updated: 2026-05-26
Canonical: https://everylastmile.app/glossary/automatic-drive-tracking

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**Automatic Drive Tracking** is the umbrella term for an iOS app that detects, records, and classifies a vehicle trip with no user input — the phone notices you started driving, records the route, and ends the trip when you park.

The underlying technology is **sensor fusion**: combining low-power readings from the accelerometer, gyroscope, magnetometer, and barometer (processed by Apple's motion coprocessor, integrated into the A-series SoC since the M9 generation) with periodic GPS samples. Apple exposes this stack through the Core Motion framework — specifically `CMMotionActivityManager` (which classifies activity as automotive, walking, cycling, or stationary) and the location services APIs.

**Why this matters for a mileage tracker.** Continuous GPS polling drains a battery in hours. The motion coprocessor runs on a dedicated low-power chip and tells the main CPU _when_ to wake up the GPS. The result: a tracker that runs all day, every day, in the background, without killing your phone or your patience. This is the architecture ELM is built on; it is also what underlies Apple Maps' driving detection and the Health app's workout auto-start.

**A common misconception.** "ADT" is a category, not a product. ELM is one implementation; competing trackers use similar approaches. What differs is the trip-classification logic (is this drive business or personal?), the §274(d) audit trail produced, and whether the data ever leaves the device.

**A worked scenario.** Robin is a real-estate agent who drives 14 client showings on a Tuesday. With manual logging she would need to open an app 28 times (start + stop). With ADT, the phone records all 14 drives in the background; her saved-place rules classify the showings as business on their own, and the trip log is complete. At the first-half 2026 business rate of 72.5¢ per mile (which rises to 76¢ for miles driven July 1–Dec 31 after the mid-year increase), the average showing-day drive of 47 miles becomes a $34.08 deduction logged with zero friction.