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MRI Guard

Protect your devices from MRI

iPhoneApple Watch10 languages

Launch offer: the full version at an introductory price, for a limited time.

Your iPhone and Apple Watch are among your most important and most expensive companions — photos, chats, cards, half your life. And of all places, their most dangerous opponent waits at your workplace: an MRI scanner's magnet is never off. One step too far, and the field can wipe or damage your device — or tear it from your hand in an instant. We all know to be careful — and still it happens: an emergency, stress, one moment of distraction — and a device that holds so much is done for.

Made for everyone who regularly deals with MRI: radiographers and MRI technologists, radiologists, other physicians and nurses in hospitals and practices, service engineers and researchers — and patients with a smartphone in their pocket.

With MRI Guard, your devices protect themselves: the app reads the magnetic field around them and sounds a loud, unmistakable alarm as it climbs toward the danger zone — your moment to stop, check, and step back.

Made by an MRI physicist

MRI Guard is built by Dr. David Grodzki — MR physicist, inventor of numerous MR patents, and multi-award-winning MR innovator, including the German Future Award for Technology and Innovation (Deutscher Zukunftspreis), presented by the German Federal President. He develops MRI Guard as a hobby, outside his work at Siemens Healthineers; it is a private project and not affiliated with his employer. It's built by someone who works with these magnetic fields first-hand and is deliberately careful about what the app claims: a smart awareness aid — never a replacement for patient and staff screening, the MR safety zones, ferromagnetic detection systems or your site's MR safety officer.

What it does

Live magnetic-field reading with a clear colour scale (green → red)
Adjustable alarm threshold — default 3 mT, the EU action level for attraction and projectile risk (Directive 2013/35/EU); adjustable from 0.1 to 5 mT
Loud alarm and vibration when the field crosses your threshold
Keeps monitoring in the background, even with the screen locked
Smart Alarm against false alarms — on by default
Units in microtesla (µT), millitesla (mT) or gauss (G)
Automatic start or arrival reminder at your saved workplace (iPhone), plus Shortcuts and Siri
Share your workplaces and settings with colleagues as a link or QR code (iPhone)
Pauses itself while the device is charging — induction chargers create strong fields of their own — and resumes the moment you unplug
Warns you clearly when iOS Low Power Mode is on, which can delay background monitoring

iPhone & Apple Watch

The iPhone is the heart of MRI Guard — and where the app is at its best: once started, it keeps measuring while it sits in your pocket, and it can start by itself when you arrive at work.

Apple Watch — the MRI shift: start a shift on the watch and it measures the magnetic field for the whole shift, screen on or off, and alarms on your wrist. The shift is recorded as a workout — heart rate, distance, energy, steps, stand time, daylight and sound level — and, unless you discard it, saved to Health as a Walking (indoor) workout; summary and history live on the iPhone. Leave the workplace and the watch asks whether to end. Uses HealthKit; everything stays on your device. Full version.

Android version

An Android version is on our roadmap, and we’ve already completed an initial technical evaluation.

Because Android devices vary widely in their hardware, magnetic sensors, and background-app behavior, building a reliable safety alarm requires extensive testing across different manufacturers and device models.

Reliability is essential to us. We won’t release an alarm that works on some phones but could silently fail on others. That’s why we’re taking the time to properly validate the Android version before making it available.

We can’t share a release date yet, but Android is firmly on our roadmap.

Arriving at work — good to know

Save your workplace once and automatic start arms monitoring hands-free the moment you arrive — a notification confirms it. Prefer to decide yourself? Switch to the arrival reminder, where one tap on the notification starts monitoring instead. Either way it stops by itself when you leave. This uses Apple's geofencing; for reliable detection allow Always location access with Precise Location on, keep Wi-Fi enabled (iOS uses it to recognise places, even without a connection), and avoid Low Power Mode. iOS typically reports an arrival one to three minutes after you reach a saved place — and opening the app always starts monitoring right away. For large buildings you can increase a place's detection radius in the app.

Private by design

No account. No sign-in. Your saved locations stay on your device, and the app never uploads them — share them with a colleague, and they travel only inside the link you send. The app can share anonymous, aggregate usage statistics to help improve it — you can turn that off anytime in Settings. See our Privacy Policy.

Please read. MRI Guard is an awareness aid — not a certified safety device or medical instrument, and no substitute for screening, the MR safety zones, ferromagnetic detection systems or the instructions of your MR safety officer. The magnetic sensor in a phone or watch is uncalibrated and saturates at a few millitesla, so it cannot measure strong fields accurately and may not react in every situation. Never rely on it for safety-critical decisions. Always follow your site's MR safety rules and use approved measuring equipment. You are responsible for your own safety and your devices.

Support

Questions, feedback, or a problem? Email info@papaetfilles.com.