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Design a smart doorbell like ring

PremiumIoT systemMedium

  • Video doorbell
  • Battery budget
  • WebRTC

Quick answer

This ioT system interview question asks you to design a smart doorbell like ring. 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 doorbell like Ring: a battery or wired video doorbell that alerts the owner's phone when someone presses it, records motion clips to the cloud, and supports live view with two-way talk. The hard parts are waking a sleeping battery device fast, months of battery life and petabytes of video.

The doorbell has a camera, a microphone and speaker, a motion sensor (PIR), a button and Wi-Fi. Battery models sleep most of the time and wake on motion, on a button press, or when the owner opens live view. Owners share access with family.

What must a smart doorbell like ring do?

  • Press alert: A button press rings every shared phone within 3 seconds.
  • Motion clips: Motion starts a 20-second recording that is uploaded while it records and kept for 30 days.
3 more requirementsUnlock to see all

How well must it do it?

  • Battery: A battery doorbell lasts at least 3 months on a 6,000 mAh pack at 5 events per day.
  • Theft proof: A clip already recorded must survive if the doorbell is ripped off the wall mid-event.
2 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

  • Video doorbell
  • Battery budget
  • WebRTC
  • Push notifications
  • Wi fi power save
  • Video storage

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 doorbell like ring 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.

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Updated · Written by the SevyDevy team

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