A Watchdog Timer Is Needed in Every Embedded Device

Many embedded devices fail in the field because they lack one simple safeguard — a watchdog timer.

Without it, even a small software hang can make your product unresponsive until a customer flips the breaker.

That’s exactly what happened to me today.

Why Watchdog Timer Matters in Embedded Systems

I had to power cycle my house today.

Not because of a storm or electrical issue.

Because a smart light switch stopped responding weeks ago — and cutting power to the misbehaving device was the only way to bring it back.

This is what happens when embedded devices ship without a proper watchdog timer.

A watchdog timer is your firmware’s last line of defense against getting stuck. It’s a hardware timer that expects your software to periodically “pet” it.

Miss that deadline? The system automatically resets.

The dimmer in my kitchen? It got into a bad state and stayed there.
No recovery mechanism. No failsafe. Just a permanently unresponsive device until I killed power to the house.

Common Watchdog Timer Design Mistakes

Too many IoT products rely on “it’ll probably be fine” as a design strategy.
They ship without watchdogs, or with watchdogs implemented incorrectly — tied to the same clock as the MCU, or disabled in release builds.

The result? Devices that hang indefinitely, forcing users to power cycle. How ridiculous is it that I had to go into the utility room, open my power panel, flip the kitchen breaker, wait ten seconds, and flip it back on?

It should NEVER happen!

Five Best Practices for Implementing Watchdog Timers

Here’s how to design watchdogs that actually work in the field.

1. Use an Independent Watchdog Timer

Run the watchdog timer off an independent low-speed oscillator.
Add an external supervisor or watchdog IC for true last-resort recovery if clocks or the MCU lock up.

2. Tier Your Watchdogs with a “Phone Home” Timeout

Layering watchdogs improves robustness. For example, in space systems, we often include:

• An independent watchdog inside the MCU
• A fixed MCU watchdog (fires once per day)
• The “phone home” watchdog that resets the system once every few weeks

This multi-layered approach catches both transient and long-duration hangs.

3. Set Realistic Timeout Values

Too short and you’ll get false resets during legitimate operations.
Too long and you won’t catch hangs fast enough.

A good starting point is 2–3× your longest expected task duration.

4. Use a Task Monitor Pattern

Have each critical task set a flag when it runs.
The watchdog task only pets the timer if all flags are set within the timeout period.
This pattern catches individual task hangs without resetting healthy systems.

5. Log Reset Reasons

When the watchdog fires, write the cause to non-volatile memory before resetting.
This telemetry is gold for debugging field issues and tracking firmware reliability.

The Real-World Cost of Ignoring a Watchdog Timer

The IoT space is full of devices that hang and never recover.
No self-healing. No diagnostics. No user confidence.

Don’t ship products that require a power cycle to fix a software bug.
Design a robust watchdog timer in your embedded systems from the start — it’s your best insurance policy against failure in the field.

Your customers won’t debug your firmware.
They’ll just buy a different product.

Final Thoughts

Implementing a watchdog timer in embedded systems isn’t optional — it’s the foundation of reliable, self-recovering firmware.

When done right, it turns potential product recalls into seamless recoveries your customers never notice.

Want more real-world embedded insights like this?

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