When building IoT devices that just work — without relying on third-party APIs, proprietary cloud platforms, or black-box firmware — the choice of operating system matters more than ever.
That’s where Zephyr RTOS enters the conversation.
Zephyr is a lightweight, open-source real-time operating system (RTOS) designed specifically for embedded and IoT devices. Backed by the Linux Foundation and supported by major players like Intel, Nordic, and NXP, Zephyr is quickly becoming a go-to choice for developers who value control, modularity, and local-first design.
Personally, I stumbled onto Zephyr while searching for a more transparent alternative to FreeRTOS for a home-grown smart sensor project. What I found was not just an OS, but a well-structured ecosystem that balances flexibility with long-term maintainability.
In this review, we’ll look at what makes Zephyr so appealing for modern IoT projects, how it compares with other open-source RTOS options, and whether it deserves a place in your development toolbox.
What is Zephyr RTOS?
Zephyr RTOS is a scalable, open-source real-time operating system designed for embedded and IoT devices. Developed under the umbrella of the Linux Foundation, Zephyr is licensed under Apache 2.0, making it a true open-source platform with a strong emphasis on security, modularity, and long-term support.
At its core, Zephyr is built for resource-constrained devices, including microcontrollers and low-power wireless chips. It supports a wide range of hardware architectures including ARM Cortex-M, RISC-V, x86, ARC, and more — making it an incredibly flexible choice for developers working across different platforms.
Unlike many other RTOS options, Zephyr is more than just a kernel. It comes with a rich set of features out of the box:
- Integrated networking stack (IPv4, IPv6, BLE, Thread, LoRa, and more)
- Built-in support for device management and over-the-air (OTA) updates
- Configurable security features like secure boot and memory protection
- Toolchain and build system based on CMake and Python (using the
westCLI tool)
It’s especially appealing to developers who want to build API-free, locally controlled IoT devices — without vendor lock-in or dependency on cloud platforms.
Why Zephyr is Great for IoT
Zephyr RTOS has been steadily gaining traction in the IoT developer community — and for good reason. It’s purpose-built to solve the exact challenges that modern IoT projects face: limited hardware resources, complex networking needs, and a growing demand for local control and security.
Here’s why Zephyr stands out for embedded and IoT development:
Modular and Lightweight
Zephyr is designed with modularity at its core. You only compile and include the features you actually need for your project. This keeps the binary size small and makes it ideal for ultra-low-power devices, where every kilobyte matters.
Built-in Connectivity
Out of the box, Zephyr includes a full-featured networking stack with support for:
- IPv4 / IPv6
- Bluetooth Low Energy (BLE)
- Thread and 6LoWPAN
- LoRa and IEEE 802.15.4
- MQTT, CoAP, HTTP, and WebSocket protocols
This means you can build complex, connected devices — completely cloud-optional — with native support for local protocols.
True Open-Source Flexibility
Zephyr is released under the Apache 2.0 license, so it’s not just free to use — it’s free to modify, distribute, and integrate without restrictions. That’s a big win for projects that need full control over their firmware or aim to avoid proprietary codebases.
Strong Hardware Ecosystem
With support for over 450 boards (and growing), Zephyr is compatible with popular microcontrollers from:
- Nordic Semiconductor (nRF52, nRF53, nRF91)
- STMicroelectronics (STM32 series)
- NXP, Intel, and others
Whether you’re building a BLE sensor or a Thread-based smart home device, chances are Zephyr already supports your hardware.
Zephyr vs FreeRTOS vs RIOT OS
If you’re exploring open-source operating systems for IoT, you’ve likely come across FreeRTOS and RIOT OS alongside Zephyr. Each has its strengths and limitations, and understanding these differences can help you choose the right one for your specific project.
Here’s a high-level comparison:
| Feature | Zephyr RTOS | FreeRTOS | RIOT OS |
|---|---|---|---|
| License | Apache 2.0 | MIT (Amazon-managed) | LGPL |
| Kernel Type | Preemptive RTOS | Preemptive RTOS | Microkernel |
| Hardware Support | 450+ boards, multi-arch | Wide, mostly ARM-based | Wide, mostly ARM & MSP430 |
| Connectivity Stack | Built-in (BLE, Thread, LoRa, etc.) | Limited, external libraries | Good (IPv6, 6LoWPAN, CoAP, etc.) |
| Security Features | Built-in secure boot, stack canaries, sandboxing | Basic | Moderate |
| Community & Ecosystem | Growing, backed by Linux Foundation | Large, Amazon-supported | Smaller but active academic community |
| Tooling | west, CMake-based, integrates with Zephyr SDK | Make/CMake, IDE support | Make, native POSIX build support |
Key Takeaways:
- Zephyr is ideal for developers who need a flexible, full-stack RTOS with networking and security built-in. It’s a great choice for modern, connected devices that need tight control over system features.
- FreeRTOS is lightweight and simple, but it often relies on third-party libraries for networking and lacks advanced built-in features unless you use Amazon’s ecosystem.
- RIOT OS is excellent for constrained devices and is well-suited for research or academic applications, though it has a steeper learning curve for mainstream development.
Real-World Use Cases
Zephyr isn’t just a theoretical RTOS with a nice spec sheet — it’s being used in production-ready, real-world IoT applications. Its adoption by industry leaders and hobbyists alike shows how versatile and scalable it is.
Here are a few practical examples where Zephyr shines:
Nordic Semiconductor BLE Projects
Nordic’s nRF52 and nRF53 series are widely used in Bluetooth Low Energy (BLE) applications like:
- Environmental sensors
- Wearables
- Proximity beacons
Zephyr’s built-in BLE stack supports Nordic chips natively, making it easy to develop firmware without third-party SDKs or cloud tie-ins.
STMicroelectronics Smart Devices
STM32 chips are a staple in many DIY and industrial IoT applications. Zephyr runs reliably on a wide range of STM32 boards, enabling use cases like:
- Smart thermostats
- Home automation controllers
- Industrial monitoring systems
Thanks to Zephyr’s modular build system, these applications can be customized with only the features needed — keeping memory usage low.
Thread and Matter Development
With growing interest in Matter, the smart home interoperability standard, Zephyr is increasingly being used to build Matter-compatible devices over Thread. Developers working on local-first smart home hubs are pairing Zephyr with chips like the nRF5340 to create:
- Secure, vendor-agnostic smart switches
- Border routers that don’t require a cloud connection
- Locally controlled sensor networks
Zephyr’s support for the OpenThread stack and Matter SDKs positions it well for privacy-focused smart home builders.
Pros and Cons
Like any platform, Zephyr RTOS comes with its own strengths and trade-offs. Whether it’s the right fit depends on your project’s goals, your hardware, and your experience level.
Pros
1. Open Source with Apache 2.0 License
Zephyr’s permissive licensing means you can freely modify, distribute, and integrate it into commercial or personal projects — no strings attached.
2. Modular and Scalable
You only include what you need, keeping firmware size minimal. This makes Zephyr ideal for everything from small battery-powered sensors to more complex IoT gateways.
3. Rich Connectivity Stack
With support for BLE, Thread, LoRa, and standard IP protocols like MQTT and CoAP, Zephyr is ready for real-world, interoperable communication — no proprietary middleware required.
4. Broad Hardware Support
With over 450 officially supported boards, Zephyr runs on a wide variety of MCUs — including those from Nordic, ST, NXP, and others.
5. Secure by Design
Features like secure boot, stack protection, and system sandboxing are built-in, making it easier to build hardened devices without needing third-party patches.
Cons
1. Steeper Learning Curve
Zephyr isn’t as beginner-friendly as Arduino or even ESP-IDF. It requires comfort with command-line tools, CMake, and build systems.
2. Smaller Community (for now)
While growing fast, Zephyr’s community is still smaller than FreeRTOS or Arduino. This can mean fewer tutorials and less forum support.
3. Documentation Gaps
The official docs are improving, but some areas — particularly around advanced networking or custom board support — still rely heavily on GitHub issues and community posts.
Overall, the pros strongly outweigh the cons, especially for developers looking to escape vendor lock-in and build secure, local-first IoT systems.
Final Verdict
If you’re serious about building open, secure, and cloud-optional IoT systems, Zephyr RTOS is absolutely worth exploring.
It’s not the simplest platform to get started with, especially if you’re coming from Arduino or MicroPython. But the trade-off is clear: you gain complete control over your firmware, fine-tuned modularity, and built-in support for modern protocols like BLE, Thread, and LoRa — all within an open-source ecosystem that’s rapidly growing.
In a world where so many IoT devices are locked into proprietary APIs or tied to cloud platforms you can’t control, Zephyr offers something different: a transparent, community-driven way to build smart devices that still respect your design choices and your users’ privacy.
For developers who care about flexibility, scalability, and interoperability — Zephyr isn’t just another RTOS. It’s a solid foundation for the next generation of local-first IoT solutions.
Call to Action
Have you tried Zephyr in your own projects? Planning to move beyond basic firmware and dive into a full RTOS? Let me know in the comments — or send me your questions, and I’ll help however I can.
If there’s interest, I’ll follow this up with a “Getting Started with Zephyr RTOS” tutorial — from installation to building your first real device.