phyphox

Every smartphone is a scientific instrument wearing a consumer disguise. Inside that slab of glass sits an accelerometer, a gyroscope, a magnetometer, a barometer, a light sensor, and a microphone—each one a precision component that a phone normally wastes on step-counting and screen rotation. phyphox strips off the disguise.

Developed by the 2nd Institute of Physics at RWTH Aachen University in Germany, phyphox—short for “physical phone experiments”—is an academic project that behaves nothing like an academic project. There’s no institutional stiffness here, no half-finished grant-funded interface abandoned the moment the paper published. This is a polished, actively maintained tool that has quietly become a fixture in physics classrooms from secondary schools to universities. It is free, open-source, and refreshingly indifferent to monetizing its users. No ads. No account. No telemetry harvesting acceleration data to sell anyone running shoes.

The positioning is unusual because the competition barely exists. There are single-purpose sensor apps—a spirit level here, a decibel meter there—and there are expensive proprietary lab kits sold to schools with a hardware markup that would make a printer company blush. phyphox occupies the gap between them: a general-purpose measurement platform that treats a phone’s sensors as a unified laboratory rather than a grab-bag of party tricks.

The pitch is simple and, crucially, credible. Point the app at a pendulum, a falling elevator, a spinning office chair, a musical note—and it records the physics in real time, graphs it as it happens, and hands over clean data on the way out. For the price of an app that costs nothing, RWTH Aachen has done something generous: they’ve democratized instrumentation that used to live behind a lab door. That matters more than the feature list suggests.

• Full Sensor Access: Direct, high-rate reads from the accelerometer, gyroscope, magnetometer, barometer, ambient light sensor, and microphone—the raw hardware, exposed and labeled, not filtered through a fitness abstraction.
• Pre-Configured Experiments: A deep library of ready-to-run experiments—speed, acceleration, magnetic field, sound frequency, and the clever acoustic stopwatch that starts and stops on sound cues—so a meaningful measurement is possible within seconds of install.
• Web Interface: Control experiments and watch live plots on any computer over Wi-Fi, no external software or drivers required. This is the feature that turns a phone on a demo table into a projector-ready teaching rig.
• Custom Experiment Editor: An online editor for building your own experiments, with real signal-processing muscle—Fourier transforms, cross-correlations, and custom math applied directly to live sensor streams.
• Standards-Based Export: Data out as Excel or CSV, so measurements flow straight into whatever analysis pipeline a lab report demands.

The Core Loop

phyphox works because it collapses the distance between phenomenon and data. Traditional physics instruction has a friction point that every teacher knows: the gap between the thing happening and the number describing it. Drop a ball, fumble with a stopwatch, eyeball a ruler, and by the time the data reaches a graph, the intuition has evaporated. phyphox closes that gap to near-zero. Motion happens, and the curve draws itself on screen while the motion is still happening. That immediacy is the whole point, and the design is built around delivering it.

Open the app and there’s a menu of experiments grouped by sensor and by concept. Pick “Acceleration (without g),” hit play, and the accelerometer streams into a live plot. Tap over to a different view—raw values, a graph, a computed magnitude—and the same data reframes itself instantly. The tabbed interface within each experiment is the smartest design decision in the app: one measurement, several simultaneous lenses. A student sees the raw numbers, the time-series graph, and the derived quantity side by side, and the relationship between them stops being abstract.

Where the Real Power Lives

The pre-built experiments are the front door. The custom editor is the whole house. This is where phyphox separates itself from every toy sensor app on the store. Users can define their own inputs, chain mathematical operations across sensor streams, run a Fourier transform on a microphone signal to pull frequencies out of a sound, or cross-correlate two signals to measure a time delay. That last capability powers the acoustic stopwatch and the famous speed-of-sound experiments—measuring how long a clap takes to travel between two points, using nothing but a phone’s microphone and some clever math.

This is real digital signal processing, exposed to anyone patient enough to learn the editor. And there’s the catch. The editor is powerful and correspondingly unforgiving. It is not a friendly drag-and-drop sandbox; it’s closer to a configuration language with a GUI wrapped around it. Beginners will not wander in and build a working experiment on instinct. But that’s a defensible trade. RWTH chose depth over hand-holding, and for the audience that matters—educators, serious students, tinkerers—it’s the right call.

The Honest Limitation

Here’s the thing nobody selling a “science lab in your pocket” wants to admit: phyphox does not teach physics. It is a measurement instrument, full stop. Hand it to a curious teenager with no guidance and they’ll get a beautiful graph of numbers they don’t understand. The app assumes the user already knows what an accelerometer measures, why the magnitude of a vector matters, and what they’re trying to prove. Without a worksheet, a lab manual, or a teacher framing the question, it’s a multimeter handed to someone who’s never seen a circuit.

That’s not a flaw so much as a boundary. A great oscilloscope doesn’t teach electronics either. But it’s the single most important thing to understand before installing, and it reframes who this app is actually for. phyphox is the instrument. The user—or their instructor—still has to supply the experiment’s meaning. RWTH does soften this with a large library of accompanying experiment guides and videos on their site, and pairing the app with that material is the difference between a toy and a curriculum.

The measurement design itself is impressive. By leveraging sensors that manufacturers calibrate for gaming and navigation, phyphox is built to pull data precise enough for real coursework. It won’t replace a lab-grade force sensor, and sensor quality varies wildly across phone models—a flagship’s barometer and a budget handset’s are not the same instrument. But for demonstrating principles and gathering usable data, the design clears the bar with room to spare.

The aesthetic is functional-Germanic: clean, restrained, faintly utilitarian, and completely uninterested in delighting anyone. This is not a criticism. A measurement tool that wasted screen space on flourishes would be a worse measurement tool. The graphs are legible, the color coding is sensible, and the live plots are designed to redraw fast enough to track quick phenomena in real time rather than reconstructing the curve after the fact. That real-time rendering is the performance-critical path, and the architecture treats it as such.

Where the design shows its age is in polish and discoverability. Menus are dense. Some experiment configurations bury their controls. The visual language is consistent but dated—more 2016 Android than 2026 anything. None of it breaks the app; all of it signals a tool built by physicists for physics, not by a design studio chasing App Store awards. That’s the right trade for what this is.

On Android, phyphox is in its natural habitat. Android’s looser sensor access and broader hardware variety mean the app can reach more sensors on more devices, and the Web Interface pairing is treated as a first-class feature. The trade-off is fragmentation: sensor availability and quality swing hard between a Pixel and a bargain-bin handset, and phyphox is only as good as the silicon underneath it.

On iOS, the experience is more uniform and, in some respects, more predictable—Apple’s tighter hardware range means fewer surprises about which sensor exists. But iOS’s stricter sensor and networking permissions occasionally add friction, particularly around the Wi-Fi Web Interface, where local network permissions have to be granted before the remote plotting works. Once configured, both platforms deliver the same core experience.

The Web Interface deserves a final note here because it transcends platform entirely. A teacher runs the experiment on a phone, projects the live plot from a laptop browser, and the whole class watches the physics unfold on a big screen. No cables, no dongles, no proprietary receiver box. It’s the closest phyphox comes to a genuine classroom superpower.

phyphox is the rare academic project that shipped a real product and kept caring about it. It doesn’t hold your hand, it won’t explain what’s being measured, and its interface won’t win any beauty contests. But it does something quietly radical: it exposes the professional-grade instrumentation already sitting in people’s pockets and asks nothing in return—no fee, no ads, no data grab. RWTH Aachen built a tool that makes physics tangible, turning abstract equations into curves that draw themselves in real time. For students, teachers, and the scientifically curious, it changes what the device in a pocket is actually for. Pair it with a good lesson plan and it earns a firm recommendation, reservations about the learning curve and dated interface notwithstanding.