Skip to main content
UNDERPRESSURE

Privacy engineering

Most health apps tell you they care about privacy and then describe, at length, the safeguards around the data they collect. Here is the whole architecture instead. The short version: nothing leaves your iPhone, because there is nowhere for it to go.

What gets sent

Nothing. UNDERPRESSURE has no account system, no backend server, and no analytics SDK. The app makes no network request that carries your health data, because there is no endpoint on the other end. This is not a setting you have to find and switch off — it is the only way the app is built.

readings        →  SwiftData, on your iPhone
context + notes →  SwiftData, on your iPhone
protocol state  →  SwiftData, on your iPhone
network         →  (no health data is transmitted)

What never leaves the device

  • Every blood pressure reading you record
  • Dates, timestamps, and daily context
  • Medication names and supplement names
  • Protocol adherence and lever rankings
  • Device identifiers (IDFA, IDFV)
  • Apple ID, iCloud account, or email
  • Any free-text you enter

Where your data lives

In SwiftData, in the app container on your iPhone, protected by the same iOS file encryption that protects everything else on the device. There is no iCloud sync and no CloudKit container, so your readings are not copied to Apple servers either. Two practical consequences follow, and you should know both: your data is not shared between your devices, and deleting the app deletes the data.

Apple Health

HealthKit access is read-only and optional. If you grant it, the app pre-fills a reading that your cuff already wrote to Health — Withings and most Bluetooth monitors do this — so you do not type the same numbers twice. UNDERPRESSURE does not write back to Health, and Apple does not give apps a way to see your Health data remotely.

What that means we cannot do

This is the honest half of the pitch. Because we hold nothing, we cannot read your readings, cannot identify you, cannot restore your history if you lose your phone, and cannot hand your data to anyone who asks — an insurer, an advertiser, or a court. The protection and the limitation are the same design decision. If cross-device sync matters more to you than this, UNDERPRESSURE is the wrong app.

This website

Separate from the app, and worth stating plainly. The site uses privacy-first analytics that set no cookies and do not track individual visitors. There are no third-party trackers, no social pixels, and no advertising tags. The site never receives health data, because the app never sends any.