Why pre-screen firmware developers before the technical panel
Two things define this work. Devices run on a battery for years, so every wake cycle costs a measurable amount of the product's life. And once shipped they are unreachable, so a failed update is a device someone has to physically visit. Developers worth hiring design for both. A short screen asks about a bug they had to fix on devices already in the field.
What actually matters when screening IoT Firmware Developer candidates
- 01
Technical depth
Probe bare-metal and RTOS work: C on ARM Cortex-M, FreeRTOS or Zephyr, interrupt priorities, DMA, I2C/SPI/UART drivers, low-power sleep modes, and BLE or LoRaWAN stacks.
- 02
Work that shipped
Ask which shipped devices carry their firmware: production volumes, bootloader and OTA update design, certification passes (FCC, CE, Bluetooth SIG), and field failure rates after release.
- 03
Diagnosis under uncertainty
Test debugging of intermittent faults: hard fault tracing with JTAG or SWD, logic analyser and oscilloscope captures, stack overflows, memory leaks, race conditions, and radio dropouts in the field.
- 04
Working across the org
Assess handoffs with hardware engineers on schematics and bring-up, plus work with cloud, mobile and QA teams on protocol contracts, MQTT payloads and test fixtures.
Pre-screening questions to ask IoT Firmware Developer candidates
12 questions grouped by what they test. Ask the same set in every screen and score answers on a consistent scale, or send them as an async video screen and compare answers side by side.
Devices in the field
3 questions01Can you describe a project you worked on from concept through to deployment?
Listen forDevices that shipped in volume, with what changed between prototype and production described honestly.
Prototypes and evaluation boards only, or no device that reached customers in any quantity.
02Can you describe your experience developing firmware for connected devices?
Listen forFirmware written from bring-up onwards, with the device lifecycle from provisioning to retirement considered.
Work limited to application layers on someone else's platform, or provisioning never handled.
03Which microcontrollers or hardware platforms have you worked with?
Listen forPlatforms used at production scale, with peripheral and errata knowledge from real board bring-up.
Platforms named from development kits only, or no experience of hardware errata.
Constraints respected
4 questions04How do you handle power management in device firmware?
Listen forA power budget calculated and measured, with sleep states and wake sources designed for battery life.
Battery life estimated from datasheets, or actual current draw never measured on hardware.
05How do you approach optimising firmware for performance and memory?
Listen forStatic allocation preferred with stack usage analysed, and flash and memory budgets tracked through development.
Dynamic allocation used freely on constrained targets, or memory headroom not tracked.
06What is your experience with real-time operating systems in this context?
Listen forTask priorities and timing reasoned about, with a real scheduling or priority problem they encountered.
Real-time systems used as a task library, with no reasoning about deadlines or stack sizing.
07What techniques do you use to handle connectivity problems on devices?
Listen forIntermittent connectivity assumed as normal, with buffering, backoff and store-and-forward all designed in.
Constant connectivity assumed, or data lost when a device is offline for an extended period.
Updates that recover
3 questions08How do you ensure the security of firmware updates delivered over the air?
Listen forSigned images verified before installation, with the signing key protected and rollback protection considered.
Unsigned updates accepted, or signature verification performed after installation rather than before.
09Can you explain your experience with bootloaders and their role in these devices?
Listen forA dual bank or recovery layout so an interrupted update leaves the device bootable and reachable.
Single image updates with no recovery path, or bricked devices treated as an acceptable rate.
10What experience do you have with security practices specific to device firmware?
Listen forSecure boot, credential storage and debug port lockdown all addressed before devices ship.
Debug interfaces left enabled in production, or credentials stored identically across every device.
Debugged remotely
2 questions11Describe a challenging bug you encountered and how you resolved it.
Listen forAn intermittent or field-only fault traced with logging, trace or hardware instrumentation.
Bugs fixed by changing things until symptoms stopped, or field faults never reproduced.
12What methods do you use to test and validate firmware before deployment?
Listen forAutomated testing on real hardware, with soak testing and edge conditions such as power loss exercised.
Testing done by hand on a desk, or power interruption during write never tested.
How to score responses
Score every candidate on the same four criteria immediately after the screen. At this stage you are shortlisting for panel interviews, not making the final call.
Technical depth
35%5Names specific MCUs and peripherals, explains ISR latency, clock trees and sleep current budgets without reaching for vague abstractions.
Work that shipped
30%5Points to devices in production, describes their OTA and rollback scheme, and knows the post-launch defect and battery-life numbers.
Diagnosis under uncertainty
20%5Walks through one nasty bug end to end, showing how instrumentation narrowed hardware, timing and software causes before the fix.
Working across the org
15%5Describes reviewing schematics pre-layout, negotiating message formats with backend teams, and giving manufacturing usable test and provisioning tooling.
A failed update is a device someone has to physically visit. A one-way video screen asks what happens when one is interrupted.
Try it on HirevireScreening FAQ
Process basics
How long should a pre-screening round for this role take?
Fifteen minutes across eight to ten questions, answered async. Enough to establish the devices they shipped, test their constraint thinking, and check update mechanism and field debugging experience.
How does this differ from an embedded engineer screen?
Connectivity and updates are the difference. Weight over-the-air update design, power budgeting for multi-year battery life and handling intermittent networks alongside the usual embedded depth.
Evaluating answers
What is the strongest signal when screening this role?
A bug fixed on deployed devices. Developers who have shipped describe the update rollout and what they did about devices that failed to take it. Anyone without that has not shipped at volume.
How do I judge their update design?
Ask what happens if an update is interrupted. Sound answers describe a dual bank layout with rollback. Anyone without a recovery path will brick devices in customers' hands.
Go deeper on this role
Sanat has been hiring since 2012 and watching the recruitment industry change up close ever since, and turned that screening process into Hirevire's video screening platform. LinkedIn
