S-Pen and Magnetic Cases: The Engineering Challenge Nobody Talks About

If you own a Samsung Galaxy Ultra and you've ever tried putting it in a magnetic case, you may have run into a puzzling problem: your S-Pen starts misbehaving. Cursor jumps across the screen. Pressure sensitivity cuts out. Hover detection goes haywire. Sometimes the pen stops registering entirely.

This isn't a coincidence, and it isn't a defect. It's physics. And understanding why it happens explains one of the most consequential engineering decisions Samsung has made over the past several years: the deliberate choice to keep magnets out of Galaxy Ultra hardware.

This post breaks down exactly how the S-Pen works, why magnets are so destructive to its performance, why Samsung still hasn't integrated Qi2 magnets into the Ultra, and how MagBak became the only case maker to actually solve this problem without sacrificing any S-Pen functionality.

How the S-Pen Actually Works: Electromagnetic Resonance 101

The S-Pen is not a simple capacitive stylus. It does not use a battery. It does not rely on Bluetooth for its core writing and drawing functions. Instead, it operates on a technology called Electromagnetic Resonance (EMR), developed and licensed by Wacom, one of the world's leading stylus technology companies.

Here's how EMR works in practice:

The Digitizer Layer

Hidden beneath the glass of every Galaxy Ultra display is a layer called the EMR digitizer. This layer consists of a dense grid of copper wire loops running both horizontally and vertically across the entire screen area. These wires are controlled by a dedicated chip that cycles the grid through two operating modes many times per second.

Power Mode and Listening Mode

In Power Mode, the digitizer sends out an electromagnetic field tuned to a specific resonant frequency. This field radiates upward through the display glass and into the space above the screen.

When the S-Pen gets close to this field, the copper coil inside the pen tip acts like the secondary coil in a transformer. It picks up the electromagnetic energy from the digitizer and converts it into electrical power. This is how the S-Pen operates with zero batteries: it literally harvests its operating power from the phone's electromagnetic field, similar in principle to how a wireless charger transfers energy to your phone.

Once energized, the pen's internal circuitry redirects that harvested energy back outward as its own distinct electromagnetic signal, carrying encoded data about tip pressure, button state, and tilt angle.

Then the digitizer immediately switches to Listening Mode: it cuts its outgoing field and starts receiving the signal coming back from the pen. By measuring the signal strength at multiple points along the wire grid simultaneously, the device triangulates the pen's exact position to sub-millimeter accuracy. It also decodes the pressure and tilt data embedded in the pen's return signal.

This entire cycle repeats hundreds of times per second, which is what gives the S-Pen its famously low latency and natural feel.

What This Precision Requires

The key thing to understand is that the S-Pen's electromagnetic signal is intentionally very weak. A stronger signal would require more power (defeating the batteryless design) and would also create interference with the display itself. The system works because the signal environment around the digitizer is controlled and quiet. The digitizer is exquisitely sensitive to the pen's faint return signal. Any outside electromagnetic noise raises the floor that signal has to rise above.

Why Magnets Destroy S-Pen Performance

Strong permanent magnets, like the neodymium magnets used in Qi2 and MagSafe accessories, create persistent static magnetic fields. These fields do not care about your S-Pen workflow. They simply exist, and they interfere with EMR in several compounding ways.

Signal Masking and Dead Zones

A strong magnet placed near the back of the phone generates a field that passes through the device body and into the digitizer layer. Because the EMR digitizer operates at low signal levels, the static field from a magnet can effectively mask the pen's return signal in the area around the magnet. The digitizer reads noise instead of signal. The result is what users describe as "dead zones" where the pen either stops responding entirely or produces erratic, jumping input.

False Air Actions and Ghost Inputs

The Galaxy S24 Ultra and S25 Ultra exposed another failure mode: magnets can trigger false S-Pen Air Actions. Air Actions are gestures the S-Pen performs via Bluetooth without touching the screen, like swiping to advance slides or zooming in on a photo. The S-Pen's Bluetooth subsystem detects motion inputs, but magnetic interference can generate spurious signals that the device interprets as intentional gestures. Users reported their phone advancing through photos or triggering app shortcuts with no deliberate pen input whatsoever.

Pressure Sensitivity Degradation

The S-Pen supports up to 4,096 levels of pressure sensitivity. That granularity comes from detecting tiny variations in the pen's electromagnetic return signal as the tip is physically compressed. When magnetic interference raises the noise floor around the digitizer, the system loses its ability to resolve those fine variations. Drawing and writing feel "stepped" or binary, which is frustrating for anyone using the S-Pen for notes, illustration, or document annotation.

Hover and Tilt Detection Failures

The S-Pen begins communicating with the digitizer before it ever touches the glass, up to approximately 10mm above the surface. This hover detection enables features like previewing links, seeing cursor position before committing a stroke, and accurate palm rejection. Magnetic interference shortens or completely eliminates this hover range, making the pen feel unresponsive until it's physically pressed against the screen.

Tilt detection (which varies brush orientation in drawing apps based on how you hold the pen) relies on the same precise signal geometry. Interference scrambles the tilt readings, making the pen appear to always be held perpendicular regardless of its actual angle.

Samsung's Deliberate Engineering Tradeoff: No Built-In Magnets

Apple introduced MagSafe with the iPhone 12 in 2020 and has included a ring of built-in magnets in every iPhone since. Qi2, the industry-standard version of this magnetic alignment system, has been broadly adopted across Android as well. So why, years later, does Samsung still ship the Galaxy Ultra without built-in Qi2 magnets?

Samsung's official answer has been slim device dimensions. Building a magnetic ring into the phone body adds thickness and competes for space with the battery, camera hardware, and structural components. That explanation has always felt incomplete given how thin modern iPhones are while still including MagSafe.

The S-Pen interference issue tells a more complete story. Integrating a permanent ring of high-strength magnets directly into the Galaxy Ultra chassis would place those magnets in permanent proximity to the EMR digitizer layer. Even with shielding attempts, a static magnetic field embedded in the phone body would be far harder to isolate than one that only appears when a user snaps on a case. Samsung would be building interference directly into the hardware stack and shipping it to every customer, whether they use the S-Pen or not.

As Android Headlines noted when the S26 Ultra launched in February 2026: "Could these persistent interference issues be the real reason Samsung hasn't integrated Qi2 magnets directly into the phone's hardware? It is purely speculative, but it's possible the company hasn't yet found a way to make a permanent internal magnet and the high-precision S-Pen coexist without compromise."

This is the tradeoff Apple doesn't have to make. The Apple Pencil uses AES (Active Electrostatic) technology, which is less susceptible to magnetic interference than EMR. Samsung chose EMR because of its superior pressure sensitivity, hover performance, and the fact that the pen requires no charging whatsoever. Those advantages come with this specific vulnerability.

The Galaxy S26 Ultra Warning

When the Galaxy S26 Ultra launched in early 2026, Samsung shipped the device with an explicit system notification that fires when the phone detects a magnetic accessory nearby. The message reads: "Magnets in accessories can interfere with your S-Pen's signal." The phone then recommends removing the magnetic accessory if you experience writing or connection issues.

This is Samsung acknowledging in plain language what the community had been discussing for years. Magnets and the S-Pen are fundamentally in tension. The phone cannot resolve that tension for you. It can only warn you about it.

Samsung has indicated it is exploring "more advanced technology" to address the issue in future models. Until that solution arrives, Galaxy Ultra owners face a choice: magnetic ecosystem or full S-Pen functionality.

Or they did, until MagBak solved it.

How MagBak Engineered Around the Problem

MagBak's Galaxy Ultra cases carry a distinction that no other case on the market can claim: they are the only cases engineered with multi-layer magnetic shielding to support all S-Pen functions.

This is not a marketing phrase. It is the product of a genuine engineering challenge that most case manufacturers have not attempted to solve. Building a magnetic case for the Galaxy Ultra requires not just placing magnets in the case body, but actively managing the magnetic field those magnets produce so that it doesn't reach the EMR digitizer layer with enough strength to interfere.

The approach MagBak uses involves layering magnetically permeable shielding materials between the case's magnets and the phone body. These materials redirect magnetic flux, channeling it outward (where it does its job of attaching to MagSafe and Qi2 accessories) rather than inward through the glass, display stack, and into the digitizer layer.

The result: you get the full magnetic ecosystem. Qi2 wireless charging alignment, MagSafe wallet attachment, magnetic car mount snapping, and MagBak's own mounting system. And your S-Pen still works exactly as Samsung designed it, with full pressure sensitivity, hover detection, tilt recognition, and Air Actions intact.

The MagBak Galaxy Ultra Case

The Elite case is where MagBak's engineering ambitions become apparent. The Elite starts with a polycarbonate frame overmolded with TPU, giving it a more structured feel than the Classic. But the differentiating features go well beyond materials:

• Built-in kickstand: An integrated kickstand supports portrait and landscape orientations at multiple angles, making the Galaxy Ultra a genuinely useful desk or table display without needing a separate stand.
• Embedded finger loop: A deployable finger loop extends from the back of the case and stows cleanly when not in use. It deploys and retracts with a single motion and does not block wireless charging when stowed.
• Pinky pillow: A raised ergonomic ridge along the lower edge of the case provides natural support for your pinky finger during one-handed use. On a device as large as the Galaxy Ultra, this is not a minor comfort feature. It is the difference between comfortable extended use and hand fatigue.
• Swappable accent colors: The Elite's trim elements are replaceable, allowing you to change the accent color of the case without buying a new case. Accent Color Packs are available separately, making the Elite a case you can genuinely customize to your personal style.

MagBak has verified full compatibility with phone calls, cellular data, WiFi, GPS navigation, wireless charging, Bluetooth, mobile payments, and the compass. And crucially: full S-Pen compatibility. All four of the tested functions that other magnetic cases break remain completely intact.

What to Look for When Choosing a Magnetic Case for Your Galaxy Ultra

If you're shopping for a magnetic case for your Galaxy S25 Ultra or Galaxy S26 Ultra and you use the S-Pen regularly, here's what to evaluate:

Does the manufacturer specifically address S-Pen compatibility?

Most magnetic case manufacturers do not. They may include a general warning (required to disclose the known interference issue) or say nothing at all. If the product listing doesn't explicitly describe engineering work done to protect S-Pen functionality, assume that work wasn't done.

What shielding method is described?

Vague claims about "S-Pen support" are not the same as documented multi-layer magnetic shielding. Look for specifics about how the manufacturer managed the magnetic field around the digitizer area.

Does the case support the full feature set?

Hover detection (the pen working before it touches the glass) is one of the first features degraded by magnetic interference. Pressure sensitivity at the highest levels is another. If reviews or descriptions only mention "basic S-Pen functions work," that's a signal that the implementation is partial.

Is the magnet strength appropriate?

Cases that use weaker magnets to reduce interference may attach to accessories poorly or not at all. N52 neodymium magnets, the grade used in true Qi2 accessories, require more careful shielding than weaker alternatives. Cases using inadequate magnets may claim S-Pen compatibility while also failing to actually work with the magnetic ecosystem you want.

The Bottom Line

The S-Pen is the defining feature of the Galaxy Ultra lineup. It is what separates these phones from every other large-format Android device. Samsung has made significant engineering commitments to the S-Pen's EMR system across every generation, accepting the tradeoff of not embedding Qi2 magnets in the hardware rather than compromise stylus performance.

That tradeoff doesn't have to cascade into your case choice. MagBak has done the engineering work that other case makers haven't: building a magnetic ecosystem case that genuinely protects all S-Pen functions, not just some of them, and not just sometimes.

If you want to use magnetic accessories with your Galaxy Ultra without giving up the S-Pen, there's one case to look at.

— The MagBak Team