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House ECG treats a building's vibration pattern much like a long-term electrocardiogram: the value comes from repeatable measurements at the same location and from observing change over time, not from declaring safety from one short recording.

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Method version: Welch directional v0.3.0

Last updated: August 15, 2026

1. Professional and research basis

House ECG is guided by civil-engineering practice and published signal-processing methods. The product lead is a National Taiwan University–trained professional civil engineer who has participated in earthquake-related work since Taiwan's 1999 Chi-Chi earthquake.

The MVP deliberately uses a transparent, deterministic process rather than a neural network. This makes every decision rule reviewable while field data are collected.

2. Intended use

House ECG is designed for a dedicated iPhone 8 or later, continuously powered and kept in the foreground during monitoring.

For a multi-unit building, the phone should be placed face up on a floor at least one level above the ground floor, within about 5 cm of a wall, secured with thin 3M double-sided tape and preferably a rigid phone case. A light paper box or cloth may cover it to reduce dirt and accidental kicks. For a detached house, placement on or rigidly connected to a structural beam is preferred.

Moving the phone changes the structural path and local response. Therefore, any move ends the previous installation and starts a new long-term initial value, even if GPS appears unchanged or the phone only changes floors.

3. Measurement flow

  1. The iPhone samples motion at 50 measurements per second.
  2. A low-cost monitor watches for unusual motion.
  3. After a trigger, the app performs the full deterministic analysis.
  4. Every candidate event is retained locally so the user can label it as earthquake-like, false alarm, or uncertain.
  5. A notification is sent only for a high-confidence local event or an event confirmed by an external earthquake catalog. Other events remain unconfirmed and can be reviewed locally.

The 50 Hz rate is sufficient for the current 0.3–10 Hz building-vibration band while leaving room for filtering. It is not presented as laboratory-instrument equivalence.

4. Three directions and phone heading

The app keeps three signed motion directions separate. When magnetic heading and phone orientation are reliable, the horizontal phone axes are rotated to North–South and East–West, and the gravity direction is treated as vertical.