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Design item tracking like apple AirTag

PremiumIoT systemHard

  • BLE
  • Crowdsourced finder network
  • Rotating keys

Quick answer

This ioT system interview question asks you to design item tracking like apple AirTag. 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 item tracking like Apple AirTag: coin-cell BLE tags that owners attach to keys and bags, found through a crowd of passing phones that report where they heard the tag. The hard parts are a one-year battery, keeping locations private even from the server, and stopping tags from being used to stalk people.

A tag has a BLE radio, an ultra-wideband (UWB) chip for precise direction finding, NFC and a small speaker. It has no GPS and no internet. Any of about 1 billion phones that hears a tag can report its location; only the owner can read that report.

What must the system do?

  • Nearby finding: The owner's phone shows distance and direction within about 10 m, and can make the tag play a sound.
  • Crowd finding: When the tag is away from the owner, passing phones report where they heard it, and the owner sees recent locations.
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How well must it do it?

  • Battery: One year on a CR2032 coin cell (about 220 mAh).
  • Privacy: The server can never learn a tag's location, its owner, or which finder reported it.
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What scale should you design for?

Use these numbers in your estimates.

The scale numbers unlock with this questionUnlock

Key concepts

  • BLE
  • Crowdsourced finder network
  • Rotating keys
  • End to end encryption
  • Anti stalking
  • UWB

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 item tracking like apple AirTag and explain your choices the way you would in an interview.
Is this question asked at entry level?
It is marked Hard. It suits engineers preparing for senior interviews, where you are expected to drive the discussion and go deep on trade-offs.
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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