Smart Item Tracker – How It Works

Overview

What does this device actually do?

It watches your belongings 24/7

Five sensors are placed around a tray or shelf. Each sensor watches one item — your wallet, earbuds, glasses, and two sets of keys.

Think of it like this: imagine a mat by your door that can "feel" whether each item is sitting on it.

It listens for your phone on Wi-Fi

Your phone constantly sends tiny invisible signals over Wi-Fi. The device listens for your specific phone and knows when you're home or away.

Think of it like this: your phone is constantly whispering its name. This device is tuned to hear only your phone's whisper.

It sends you a phone notification

Using the Blynk app, it pushes a message to your phone. Whether you just walked in or walked out — it tells you what's missing.

Think of it like this: a helpful friend at the door who says "Hey, you forgot your glasses!"

It shows the status on a small screen

A tiny display on the device shows a live list of all five items — FOUND or MISSING — updated every 300 milliseconds (about 3 times per second).

Think of it like this: a scoreboard for your belongings, updating in near-real-time.

It glows a rainbow while it works

A strip of 8 colour LEDs slowly cycles through all colours — just to show you the device is alive and running normally.

Think of it like this: a heartbeat light — if the rainbow stops, something's wrong.

The sensors

How does each item get detected?

👕

Wallet

Ultrasonic sensor 1

Sends a sound pulse and measures how long it takes to bounce back. If something is close, the wallet is there.

👓

Glasses

Ultrasonic sensor 2

Same sound-bounce trick as the wallet sensor, just aimed at a different spot on the tray.

🎧

Earbuds

Infrared (IR) sensor

Shines an invisible light beam. When the earbuds case sits there, it blocks the beam — detected!

🔑

Key 1

Push button

A simple button. When you hang your key on a hook, it presses the button. Key on hook = button pressed = found.

🔒

Key 2

Push button

Same as Key 1 — a second hook button for a spare key, partner's key, or car key.

The brain

How does it decide what to do?

Step 1 — Power on & connect

When plugged in, the device starts up, connects to your Wi-Fi, links to the Blynk cloud service, and turns on all the sensors. Takes a few seconds.

Step 2 — Listen for your phone

In the background, it scans Wi-Fi for your phone's unique ID. The moment it hears your phone, it knows you're home.

Decision point: Is this the right phone?

Every phone has a unique "address" (like a postal address for Wi-Fi). The device is pre-programmed with your phone's address and ignores all others.

Step 3 — You arrived home

Phone detected for the first time? It checks which items are missing from the tray and sends a "Welcome home!" notification listing what needs to go back.

👋

Welcome home notification

"Welcome home! Please put your items back: [Wallet] [Earbuds]"

🚤

Nothing missing? No message

If everything is already on the tray, the device stays quiet. No need to bother you.

Step 4 — Watching the clock

Once your phone is spotted, the device keeps a timer. Every time it hears your phone, it resets the timer to zero. If 10 seconds pass with no signal from your phone — you've left the house.

Decision point: Has your phone gone quiet for 10 seconds?

Yes → you've left. No → you're still home, keep watching.

Step 5 — You left the house

Phone gone? It checks the tray one last time. If items are still there, it sends a "wait!" alert. If the tray is clear, it wishes you a great day.

⚠️

Forgot something!

"Wait! You left items behind: [Glasses] [Key 1]"

🌞

All clear

"Goodbye! Have a great day :)"

Step 6 — Back to watching

After sending a notification, everything resets. The device goes back to listening for your phone and checking the tray — ready for your next trip.