Last Echo

A zero-knowledge dead man's switch powered by Amazon Alexa, ensuring your final words reach loved ones when life goes silent.

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Inspiration

A while ago, I started thinking about how much of our lives are stored digitally—from account credentials to personal notes and memories. But if something sudden ever happened to me, almost all of that would vanish, and the things I wished I had told my parents or closest friends would never be delivered.

Most "dead man's switches" out there feel grim and stressful to use, requiring you to click weekly email links or log into an app. We wanted something completely different. Since Amazon Echo devices are already part of our daily home environment, why not let Alexa be a quiet, thoughtful guardian? Simply saying "Alexa, I'm okay" while making morning coffee should be enough to keep your digital legacy safe. That was the spark behind LastEcho.

What it does

LastEcho is an automated digital closure protocol that pairs an encrypted vault with ambient Alexa voice check-ins:

  • Effortless Alexa Voice Heartbeat: Instead of opening apps or logging into dashboards, users reset their check-in timer simply by talking to Alexa naturally: "Alexa, tell LastEcho I am doing fine" or "Alexa, I'm okay".
  • Client-Side Zero-Knowledge Encryption: When creating a farewell note or emergency instruction, the text is encrypted inside the browser using AES-GCM 256-bit before anything hits the database. The server never sees the raw message or the password.
  • Real Automated Dispatch: If someone stops checking in past their chosen threshold (e.g. 30 days + a 7-day grace window), the protocol kicks in. It automatically emails a clean, secure access link straight to the designated recipient's Gmail inbox.
  • Built-in Time Machine Sandbox: Because hackathon judges can't wait 30 days to test the switch, we built a sandbox simulator with +7, +14, +31, and +40 day jumps to watch the system shift from active to triggered in real time.

How we built it

  • Frontend: Clean dashboard built with HTML5, Vanilla CSS, and modern JavaScript. Includes a dynamic radar visualization and an in-browser Web Speech API simulator for testing voice intents directly on a laptop.
  • Cryptography: Used the browser's native Web Crypto API for client-side key derivation (PBKDF2) and AES-GCM encryption.
  • Backend: Built with Node.js and Express to track heartbeat timestamps, audit logs, and trigger delivery rules.
  • Alexa Skill: Set up custom interaction models and intents in the Alexa Developer Console, wired up to an AWS Lambda handler (alexa-skill-lambda.js).
  • Email Delivery: Integrated Nodemailer with SMTP/Gmail to send styled HTML letters to recipients whenever the protocol triggers, backed by a visual fallback preview for offline presenting.

Challenges we ran into

The hardest part was balancing security with human comfort. We didn't want the user interface to feel depressing or clinical. We spent a lot of time getting the conversational tone of Alexa's responses right so it feels reassuring rather than alarming.

Technically, making sure zero-knowledge encryption worked smoothly across both client-side creation and recipient decryption took quite a few rounds of debugging with Web Crypto buffer formatting (ArrayBuffers, IVs, and Base64 conversions).

Accomplishments that we're proud of

  • Connecting an ambient smart home speaker directly to client-side cryptographic security.
  • Having a complete end-to-end flow working live: speaking to Alexa, resetting the heartbeat, fast-forwarding time in the sandbox, and seeing a real email pop up in Gmail with a decryptable letter.

What we learned

We realized how natural ambient voice interfaces are for long-term health and wellness protocols. People easily forget about smartphone apps or emails, but voice check-ins with an Echo device blend effortlessly into everyday routines.

What's next for LastEcho

  • Adding support for Alexa Presentation Language (APL) so Echo Show devices can display gentle visual reminders on their screens.
  • Multi-party verification: requiring two trusted contacts to verify an emergency before critical financial or legal capsules are unlocked.

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