MRI Guard — Press kit

In one sentence

MRI Guard turns the magnetometer in an iPhone or Apple Watch into a personal alarm for the one hazard every MRI department knows and still gets caught by: a phone or watch carried too close to the scanner.

50 words

Near an MRI magnet a phone or watch is wiped, damaged or pulled from the hand in a fraction of a second. MRI Guard measures the magnetic field around the device and sounds a loud alarm as it climbs toward the danger zone — on the iPhone from the pocket, on the Apple Watch all shift long.

150 words

MRI Guard is a magnetic-field alarm for people who work around MRI scanners: radiographers and technologists, radiologists, nurses, physicists and service engineers. The app reads the magnetometer built into every iPhone and Apple Watch and sounds a loud, unmistakable alarm — as a critical alert, through Silent and Focus — when the field crosses a threshold. The default is 3 mT, the EU action level for attraction and projectile risk (Directive 2013/35/EU); it is adjustable from 0.1 to 5 mT.

On the iPhone, monitoring starts by itself on arrival at a saved workplace and keeps measuring from the pocket; workplaces and settings can be shared with colleagues by link or QR code. On the Apple Watch, an MRI shift is a real workout: the field is measured on the wrist for the whole shift, screen on or off, and the shift is saved to Health with heart rate, distance, energy and a log of every approach to the magnet.

MRI Guard is built by an MR physicist as a hobby, outside his work at Siemens Healthineers — a private project, independent of his employer — and is deliberately honest about its limits: an awareness aid, not a certified safety device — no substitute for screening, the MR safety zones or ferromagnetic detection. Available in ten languages. One purchase, no subscription.

Auf Deutsch

Ein Satz

MRI Guard macht aus dem Magnetometer in iPhone und Apple Watch einen persönlichen Alarm für die eine Gefahr, die jede MRT-Abteilung kennt und die trotzdem immer wieder passiert: ein Handy oder eine Uhr, die dem Scanner zu nahe kommt.

50 Wörter

In der Nähe eines MRT-Magneten wird ein Handy oder eine Uhr in Sekundenbruchteilen gelöscht, beschädigt oder aus der Hand gerissen. MRI Guard misst das Magnetfeld um das Gerät und schlägt laut Alarm, wenn es Richtung Gefahrenzone steigt — auf dem iPhone aus der Tasche, auf der Apple Watch die ganze Schicht lang.

150 Wörter

MRI Guard ist ein Magnetfeld-Alarm für Menschen, die an MRT-Scannern arbeiten: MTRA und MTR, Radiologinnen und Radiologen, Pflegekräfte, Physiker und Servicetechniker. Die App liest den Magnetometer, der in jedem iPhone und jeder Apple Watch steckt, und schlägt laut und unüberhörbar Alarm — als kritischer Hinweis, durch Stummschalter und Fokus hindurch —, wenn das Feld einen Schwellwert überschreitet. Voreingestellt sind 3 mT, der EU-Aktionswert für Anziehung und Projektilrisiko (Richtlinie 2013/35/EU); einstellbar von 0,1 bis 5 mT.

Auf dem iPhone startet die Überwachung bei der Ankunft am gespeicherten Arbeitsplatz von selbst und misst aus der Tasche weiter; Arbeitsplätze und Einstellungen lassen sich per Link oder QR-Code mit Kolleginnen und Kollegen teilen. Auf der Apple Watch ist eine MRT-Schicht ein echtes Training: Das Feld wird die ganze Schicht am Handgelenk gemessen, auch bei dunklem Display, und die Schicht landet mit Puls, Strecke, Kalorien und jeder Annäherung an den Magneten in Health.

MRI Guard stammt von einem MR-Physiker, der es als Hobby außerhalb seiner Tätigkeit bei Siemens Healthineers entwickelt — ein privates Projekt, unabhängig von seinem Arbeitgeber —, und ist bewusst ehrlich über seine Grenzen: ein Hilfsmittel zur Orientierung, kein zertifiziertes Sicherheitsgerät — kein Ersatz für Screening, die MR-Sicherheitszonen oder Ferromagnet-Detektoren. In zehn Sprachen. Einmal kaufen, kein Abo.

The story

Twenty years beside MRI magnets, dozens of patents, the German Future Prize — and still the same accident every year in every department: a colleague's phone or watch pulled into the scanner. Apple put a magnetometer into every iPhone and Watch; nobody had turned it into a warning. MRI Guard is one physicist's answer, measured on his own scanner and worn on his own wrist.

About the developer

Dr. David Grodzki is an MR physicist and inventor of numerous MRI patents. In 2023 he received the Deutscher Zukunftspreis, the German Federal President's award for technology and innovation. MRI Guard is his hobby project, developed outside his work at Siemens Healthineers and not affiliated with his employer, built and tested at the scanner. He speaks about the physics of stray fields, what a smartphone magnetometer can and cannot do, and why the App Store's rules for a Watch app took two rejections to get right.

Facts

Name

MRI Guard

Platforms

iPhone (iOS 17+), Apple Watch (watchOS 10+)

Android

On the roadmap; initial technical evaluation completed. No release date yet — reliability has to be verified across manufacturers and models first. Statement below

Current version

1.3, released 30 September 2026 (1.0: 12 September 2026)

Price

Free: live reading, gauge, chart. Full version (alarm, automations, Apple Watch, Shortcuts): one-time purchase, no subscription. Introductory price until 12 November 2026.

Languages

English, German, French, Spanish, Italian, Portuguese (Brazil), Chinese (Simplified), Korean, Japanese, Arabic

Default threshold

3 mT — the EU action level for attraction and projectile risk (Directive 2013/35/EU, Annex II); adjustable 0.1–5 mT

Sensor

The device's own magnetometer; uncalibrated, saturates around 4 mT — both disclosed in the app

Alarm

Sound, vibration and a critical alert that sounds through Silent and Focus (Apple entitlement granted for the field alarm)

Apple Watch

An MRI shift is a Walking (indoor) workout recorded with HealthKit; the field is measured on the wrist for the whole shift; saved to Health unless the user discards it at the end (saved automatically after ten minutes if left unanswered)

Sharing

Workplaces, alarm and notification settings can be passed on to colleagues as a link or QR code (iPhone); the recipient sees a preview, and nothing changes until they apply it. The settings travel inside the link itself — no account, nothing uploaded by the app

Privacy

No account, no tracking, no ads. Saved places never leave the device except inside a link the user shares. Anonymous usage statistics (TelemetryDeck) can be turned off in Settings. Privacy policy

Developer

Dr. David Grodzki, Germany · info@papaetfilles.com

Links

App Store · Product page (EN) · Produktseite (DE)

App icon

Screenshots — iPhone

Click for full size (1320 × 2868). English; German versions in the ZIP.

Screenshots — Apple Watch

Why it matters — three facts to quote

• An MRI magnet is never off. Its field reaches metres beyond the scanner, and it pulls on steel with a force that grows with the cube of proximity — the last half metre is where a phone leaves the hand.
• The EU sets 3 mT as the action level for attraction and projectile risk near strong magnets (Directive 2013/35/EU). Every iPhone and Apple Watch carries a sensor that can read that field — nobody had wired it to an alarm.
• Hospital MRI shifts are walking-heavy — six to ten kilometres a day in the literature — in loud, windowless rooms. That is why the Watch records the shift as a workout with the field log inside it.

Usage guidelines

Texts, screenshots and the app icon on this page may be used freely in coverage of MRI Guard; please use the icon unaltered. Please write the name as MRI Guard (two words). MRI Guard is not affiliated with any MRI manufacturer. Review codes for the full version are available on request.