You've been here before. Deadline approaching, shoulders up around your ears, chest tight. Someone tells you to take a deep breath. So you try. And then you wonder: did that actually do anything?
Most breathwork apps are glorified timers. They show you an animation, tell you when to inhale and exhale, and leave you to guess whether your nervous system got the memo. shii·haa works differently. Instead of simply telling you when to breathe, it listens — and then shows you what your body is actually doing.
What Makes shii·haa Different
The core insight is simple but significant: breathing exercises only work if your body responds to them. The question was never how to breathe. It was always: is it working?
shii·haa answers that question in real time through two channels.
The first is your microphone. The app detects the sound of your breath — the gentle turbulence of air moving through your nose and mouth — and translates that into a live rhythm signal. No wearable required. Just breathe normally.
The second is your heart. Connect a Bluetooth chest strap — Garmin, Polar, Wahoo, or any standard BLE heart rate monitor — and the app reads your heartbeats one by one. Not an average, but a living, moment-to-moment signal that changes with every breath.
Alone, each signal tells you something. Together, they tell you something remarkable.
The Science: Respiratory Sinus Arrhythmia
Your heart rate is not steady. Even sitting still, your heartbeats speed up slightly when you inhale and slow down when you exhale. This is called Respiratory Sinus Arrhythmia (RSA) — not a medical problem, but a sign of a healthy, flexible nervous system.
The vagus nerve modulates your heart rate in sync with your breathing. When that coupling is strong, your body is in a state of physiological coherence: calm, regulated, resilient. When you're chronically stressed, that coupling weakens. Your heart rate variability flattens.
This is exactly what clinical biofeedback therapists measure — using equipment that costs thousands of euros and sessions at €150–200 each. shii·haa brings that same measurement to your phone.
When you breathe slowly — five to six breaths per minute — and your exhale is slightly longer than your inhale, your heart and breathing fall into natural resonance. You can feel it as calm clarity. With shii·haa, you can also see it.
The Stimmungs-Check: Start Where You Are
Before choosing a technique, you need to know where you're starting from. That's the Stimmungs-Check — thirty seconds of free breathing. No instructions, no pattern. Just breathe naturally while the app listens.
It analyzes:
- Breathing rate — how many breaths per minute?
- Inhale-to-exhale ratio — are your exhales longer, or are you holding without realizing?
- Regularity — consistent or erratic and shallow?
- Cardiac response — how strongly is your heart responding to each breath?
Then it gives you a personalized recommendation. Not the same sequence every day. A suggestion built on what your body just told it.
Three Signals, One Picture
Sound is the most immediate. The microphone hears the acoustics of your breath and translates it into a rhythm the app can track. It tells the app exactly when you inhale and exhale, down to the second.
Heart rate is the deeper layer. Beat by beat, the app watches how your cardiac rhythm rises and falls with your breathing. This is where the biofeedback becomes genuinely clinical.
Pattern recognition ties it together. The app recognizes the shape of your breathing — peaks, valleys, rhythm — and identifies whether you're moving toward coherence or away from it.
When all three signals agree, the picture is remarkably clear. When your breathing is smooth and your heart rises and falls in step with each breath, you're in coherence — and you can feel it, because that feeling has a name: calm.
How a Session Works
A biofeedback session in shii·haa follows a natural arc — from listening, to understanding, to guided practice.
1. Calibrate
Every session begins with a few seconds of calibration. Hold your phone about 30 cm in front of you. Be still for a moment, then breathe normally. The app learns the difference between silence and your breath — your personal baseline, in this room, right now. If you're wearing a chest strap, it picks up your resting heart rate at the same time.
2. Breathe Freely
Then you breathe — however you want. There's no timer telling you when to inhale or exhale. The app watches and listens, tracking your natural rhythm in real time. The breathing circle expands and contracts with your actual breath. The oscillograph shows your audio signal. If a chest strap is connected, your heart rate pulses alongside it.
This is the exploration phase. You discover your own pattern without being told what it should be.
3. Analyze
After the free session, shii·haa shows you what it observed:
- Breathing rate — your actual breaths per minute
- I:E ratio — how your inhale compares to your exhale
- Regularity — how consistent your rhythm was
- HRV metrics — RMSSD, SDNN, and coherence score (with chest strap)
- RSA correlation — how tightly your heart followed your breath
These aren't abstract numbers. They're a mirror. You see exactly how your body responded to your breathing — and where there's room to go deeper.
4. Your Rhythm, Your Ratios
Here is where shii·haa does something no other breathwork app does.
Every technique in the app — 4-7-8 relaxation, box breathing, coherence, resonance, and many more — has a defined ratio: the relationship between inhale, hold, exhale, and pause. A 4-7-8 pattern means inhaling for one unit, holding for 1.75 units, and exhaling for two units. That ratio is what creates the physiological effect. Not the absolute duration.
Most apps tell everyone to breathe 4 seconds in, 7 seconds hold, 8 seconds out. But if your natural inhale is 3 seconds, forcing a 4-second inhale creates tension. If your natural rhythm is slower, 4 seconds feels rushed. The technique fights your body instead of working with it.
shii·haa takes a different approach. You start by breathing a technique freely — at your own pace, guided by the ratios but not locked to a metronome. The app observes your natural tempo: how long your inhales actually take, how your body settles into the pattern. It measures your personal base rhythm.
Then, for the guided session, the app adapts the absolute timings to your rhythm. If your natural inhale is 3.2 seconds and the technique calls for a 1:1.75:2 ratio, the guided session becomes 3.2s inhale, 5.6s hold, 6.4s exhale. The ratio stays precise. The tempo becomes yours.
The app corrects the ratios — not your rhythm. If your exhale was too short relative to the pattern, it gently extends it. If your hold was cut short, it adds a moment. But the fundamental pace stays anchored to how you actually breathe.
This matters more than most people realize. The ratio between inhale and exhale determines the autonomic effect: a longer exhale activates the parasympathetic nervous system (calming), equal phases create balance (focus), emphasis on the inhale activates the sympathetic system (energy). The absolute seconds are just a vehicle for the ratio. Your body doesn't care whether you breathe in for 4 seconds or 3.2 seconds. It cares about the Gestalt of the breath.
And with the biofeedback running throughout, you can verify it in real time. Watch your HRV improve, your coherence score rise, your heart-breath coupling strengthen — all at a pace that feels natural, not forced.
That's the difference between following a timer and being guided by your own body. Proof, not hope. Your rhythm, not someone else's.
Who This Is For
Anyone who wants to know if their breathing practice is actually working.
People with anxiety who want evidence that "just breathe" actually helps. Athletes who track HRV for performance. Meditators who want to watch their nervous system settle. People with insomnia who use breathwork before bed. And curious humans who want to understand how their body works.
You don't need a clinical diagnosis. You just need to be a person with a nervous system.
Built by a Doctor, Not a Startup
shii·haa was created by Dr. Felix Zeller — an intensive care physician, emergency doctor, and clinical psychologist based in Zürich.
Felix built this because he saw what clinical biofeedback could do for patients in real distress — and then watched those same patients go home without any way to continue. The equipment was too expensive. The sessions too infrequent. The gap between clinical insight and everyday life too wide.
shii·haa is his attempt to close that gap. Not a simplified version of biofeedback, but a genuine measurement tool that happens to live in your pocket.
Try It
shiihaa.app — runs in Chrome, no install needed. iOS and Android apps also available.
A Bluetooth chest strap is optional but recommended for full biofeedback. Any standard BLE heart rate monitor works. Dana pricing — pay what you wish.
The next time you take a deep breath, you don't have to wonder if it worked. Your body will show you.
Felix Zeller is an intensive care physician, emergency doctor, and clinical psychologist based in Zürich. He built shii·haa — a breathwork and biofeedback app — with Perplexity Computer. Try it at shiihaa.app.
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