SevyDevy

Design a smart home system like Google home

PremiumIoT systemMedium

  • Matter
  • Thread
  • Device shadow

Quick answer

This ioT system interview question asks you to design a smart home system like Google home. Aim for a design that collects data from many devices and acts on it reliably, then explain device connections, ingestion, storage and trade-offs. Interviewers want to see how you handle unreliable networks, device scale and data volume.

The problem

Design a smart home system like Google Home: a hub, a phone app and a cloud service that control lights, plugs, locks and thermostats from many brands. The hard parts are keeping device state correct across app, voice and wall switch, and still working when the home internet drops.

Each home has a hub (a smart speaker or display) on Wi-Fi with a Thread border router built in. Devices join over Wi-Fi or Thread using Matter, or are reached through another brand's cloud. Users tap a tile, speak a command or let a routine run, such as "at sunset, turn on the porch light".

What must a smart home system like Google home do?

  • Control: Turn devices on or off, set levels and read their state from the app, by voice or from a routine.
  • State sync: A change made at a wall switch or in another brand's app shows up in every app and on the hub within 2 seconds.
4 more requirementsUnlock to see all

How well must it do it?

  • Latency: Local commands finish within 300 ms at p95; commands from outside the home within 1.5 s at p95.
  • Honest state: The app shows the last reported state and its age; a command stays "pending" until the device confirms it.
3 more requirementsUnlock to see all

What scale should you design for?

Use these numbers in your estimates.

The scale numbers unlock with this questionUnlock

Key concepts

  • Matter
  • Thread
  • Device shadow
  • Local control
  • MQTT
  • Cloud to cloud integration

How you’ll practise

6 short steps · save and come back any time
  1. Requirements
  2. Estimate
  3. Device and connectivity
  4. Ingestion and processing
  5. Device management and updates
  6. Wrap-up

Lala, personalized to you, gives a hint when you ask and reviews your design when you are ready.

What do interviewers look for?

In any IoT system design round.

  • Clarifies device count, message rate and payload size
  • Handles devices that go offline and reconnect
  • Plans ingestion that absorbs bursts
  • Separates hot real-time data from long-term storage
  • Covers device identity, updates and security
  • Explains what runs on the device and what runs in the cloud

Questions people ask about this interview question

Which design type is this question?
It is an ioT system question. You design a smart home system like Google home and explain your choices the way you would in an interview.
Is this question asked at entry level?
It is marked Medium. Entry-level engineers can practise it, but it expects you to reason about requirements and trade-offs, not only list components.
What should I cover first?
Start with the devices, what they send, how often and what must happen with it. Agree on scope with the interviewer before you design anything.
Can I practise it for free?
It is a premium question. Sign up and unlock it once for 10 credits; it then stays unlocked. When you finish, Lala, your personalized AI mentor, can review your design for 30 credits.

Related questions

Updated · Written by the SevyDevy team

Premium questionSign up free, then unlock it