Senior Firmware Engineer - Embedded BLE, sensor fusion, consumer IoT

Senior Firmware Engineer

ZWIM · Lisbon, Portugal · Full-time, Permanent · In-office

QUICK SUMMARY

Role: Senior Firmware Engineer — embedded BLE, sensor fusion, consumer IoT

Shipped consumer hardware product required

Location: Lisbon-based or relocating. Right to work in Portugal required, or EU passport.

ABOUT ZWIM

ZWIM is building Connected Swim Training, a new category of swim training.

Our hardware, the ZWIM Smart Paddles and our gaming platform measure stroke efficiency and power in real time, and let athletes turn training into something measurable, immersive, and addictive.

Backed by €1.4M in seed funding led by Lince Capital, we're a small, ambitious team headquartered in Lisbon, with over 20,000 users of our first at-home Swim Trainer.

We help age-group triathletes and swimmers be more consistent in their training, to swim faster, better, and with more confidence. Every session on a ZWIM Trainer gives data that compounds: Propulsive Watts, pace, distance, stroke efficiency. Our game, built in Unreal Engine 5, turns that data into something worth showing up for, day after day.

You'd be joining at the moment that matters most. This year is about turning a great prototype into a product athletes can't put down.

If you want your firmware to be felt by every user, every session, and you want to own the stack from sensor to game, this is that job.

If you're a swimmer, triathlete, runner, cyclist, or any kind of fitness fan, you'll fit in here.

WHY THIS ROLE EXISTS

Firmware has been built by a world-class external engineering partner. That relationship gave us a solid foundation: real data, real sensors, real BLE connectivity, and a product athletes are already using.

Now it's time to own it.

We're bringing firmware in-house, working alongside our external partner as we scale. Not because what we have is broken, but because the product we're building next demands it. Tighter iteration, faster debugging, closer integration between hardware and software, and a direct line from athlete feedback to firmware change.

This hire is the person who takes ownership of the stack and keeps it moving.

THE ROLE

You will be the first in-house firmware engineer at ZWIM.

The hardware is built around a low-power ARM Cortex-M4 BLE SoC, a 6-axis IMU, and a precision force sensor ADC — all communicating to our mobile app over BLE 5.0. The firmware runs sensor fusion, power algorithms, calibration, persistent storage, and over-the-air updates.

You will own that stack — maintain it, improve it, extend it, and eventually help design what comes after it.

You will work directly with the founders, the full-stack engineering team, and our external hardware partners. No layers. No waiting.

KEY RESPONSIBILITIES

• Own the firmware stack. Embedded C on an ARM Cortex-M4 BLE SoC. You keep it stable, clean, and shipping.

• BLE architecture. Custom GATT services, characteristic design, connection stability, throughput, and reliability across iOS and Android.

• Sensor integration. IMU data processing, force sensor ADC pipeline, quaternion-based sensor fusion, and calibration workflows.

• Power and reliability. Low-power states, battery life management, graceful error handling, and production robustness.

• OTA DFU. Maintain and extend over-the-air update infrastructure. Athletes must always be on the right version.

• Manufacturing tooling. Production-line flashing, calibration fixtures, serial number provisioning, and factory test utilities.

• Certification support. Work with our regulatory team on FCC, CE/RED, BLE SIG qualification, and whatever comes next as we scale markets.

• Cross-disciplinary integration. Define clean contracts between firmware data and the mobile and game layers. Be the translator between atoms and code.

WHAT WE EXPECT IN THE FIRST SIX MONTHS

• Get deep into the existing codebase alongside our external firmware partner and own it with full confidence.

• Ship at least two meaningful firmware improvements — reliability, performance, or new capability — that athletes feel directly.

• Establish the internal development, testing, and release process so the team can iterate predictably.

• Be the person the rest of engineering trusts to answer "what does the firmware actually do here?"

REQUIREMENTS

Experience

• 5+ years of professional embedded firmware engineering.

• At least one shipped consumer hardware product that real people bought and used.

• Experience across the full cycle: prototyping through production, including manufacturing tooling and post-launch support.

Technical

• Strong embedded C. You write clean, readable, maintainable firmware — not just firmware that works once.

• ARM Cortex-M4 (or equivalent low-power embedded SoC), including working with a BLE SDK or embedded RTOS.

• BLE 5.0: custom GATT services, connection management, throughput and latency optimisation, iOS and Android interoperability.

• IMU integration and sensor fusion. You know the difference between raw data and useful data.

• Low-power design: sleep states, power rail management, and battery life engineering for a consumer device.

• OTA DFU — designing and maintaining reliable over-the-air update pipelines.

• Persistent NVM storage on embedded targets.

Practical

• Self-directed. You can take ownership of an unfamiliar codebase, build context fast, and start shipping improvements.

• Strong written and verbal English. You can explain a firmware decision to a product manager and a hardware engineer in the same sentence.

• Comfortable in a small team where everyone is close to the work and the user.

• Lisbon-based or willing to relocate.

• Right to work in Portugal. Ideally already in Portugal, or EU passport holder.

NICE TO HAVES

• Hardware debug tooling — JTAG/SWD, logic analyser, BLE sniffer.

• Regulatory certification experience: FCC, CE/RED, BLE SIG qualification.

• Factory calibration fixture design or production-line test scripting.

• Daily AI tooling (Claude, Cursor, Copilot) for code scaffolding, debugging, and documentation.

• Personal interest in triathlon, swimming, or endurance sports.

NOT A FIT

• Application or backend engineers who have never written embedded C targeting a microcontroller.

• Engineers who have only worked on high-power or mains-powered systems. Battery life matters here.

• Candidates who need a large team and defined process before they can ship. We move fast with a small team.

• Someone whose embedded experience is limited to side projects or academic work. We need production firmware — real hardware, real users, real consequences.

• Remote-only candidates.

COMPENSATION AND BENEFITS

Compensation

Salary and potential equity discussed in our intro call once we understand your background, shipped work, and what you're looking for.

Time and Recovery

27 paid vacation days. Rest and recovery matter as much as performance.

Flexible hours for training and recovery. We trust you to perform your best in and out of work.

Day-to-Day

Meal allowance to fuel focus and performance.

Fitness partner discounts that support an active lifestyle.

Free access to everything we are building — train, test, and improve with the product.

Direct collaboration with athletes bringing real performance insight into how we build.

Team and community events where we train, celebrate, or just spend time together.

HOW TO APPLY - Use the "EASY APPLY"

And to strengthen you application:

Email [email protected] with:

1. One firmware project you personally shipped — hardware, what the firmware did, what broke in production and how you fixed it.

2. Two or three examples of recent work — a GitHub repo, a technical writeup, or a description of a system you designed.

3. One paragraph on what you find genuinely interesting about embedded BLE systems — not what you think we want to hear.

4. Your location, availability, and compensation expectation.

Subject line: Senior Firmware Engineer, [your name]

You've read this far. Apply now.

I read every application personally and respond within 5 business days, even if it's a no. The firmware you write will be felt by every athlete who uses ZWIM. Make it yours.

Victor, Founder & CEO — ZWIM