Project Hub /Security Surveillance & Defense/Intrusion Detection Systems/Door Ajar Alert System With Countdown Timer

Intermediate

ARDUINO

₹500 – ₹1,500

3 – 6 Hours

Partial Kit

Door Ajar Alert System With Countdown Timer

An intelligent door ajar alert system featuring a countdown timer, built with a Digispark ATtiny85 board, TM1637 4-digit display, and a reed switch.

Originally published on ElectronicsForU

View original tutorial

Parts You'll Need

This project is sourced from another site, not written by us — this list is our best match of their components against what we stock, not a verified bill of materials. Always check the original blog (linked above) for the actual parts list before buying.

Reed Switch 2×14mm Normally Open Magnetic Sensor Out of stock
Piezo Buzzer (Big) 6-12V Rs. 45.00
Jumper Wire 10 Pin Male To Male 20cm Rs. 45.00
400 Points Mini Solderless Prototype PCB Breadboard High Quality Rs. 89.00
MB102 Adjustable Breadboard Power Supply Module (3.3V & 5V) for Arduino & Raspberry Pi Rs. 139.00
Jumper Wire 10 Pin Male To Female 20cm Rs. 45.00

Selected: Rs. 0.00

We don't carry yet: Other Dev Board (Indusboard / Maixduino / misc)
7-Segment Display
Screws / Nuts / Standoffs / Hardware
9V Battery + Snap
Enclosure / Box / Case

Browse all components

How It Works

The Door Ajar Alert System with Countdown Timer monitors the physical state of a door using a normally-closed (NC) reed switch paired with a permanent magnet. When the door is closed, the magnet keeps the reed switch closed, completing a circuit that signals the Digispark USB development board (powered by an Atmel ATtiny85 microcontroller) that the door is secure. If the door opens, the magnet moves away, causing the reed switch to open. This state change triggers the ATtiny85 microcontroller to begin running a countdown timer. While the timer counts down, the elapsed or remaining time is rendered visually on a TM1637 4-digit 7-segment LED display module, driven by the DigitalTube library in the Arduino IDE. If the door remains open and the countdown reaches zero before the door is shut again, the microcontroller activates a piezobuzzer to emit an audible alert. The entire compact circuit is powered by a 9V alkaline battery pack and housed neatly inside a rigid plastic box, ensuring the electronics are protected while monitoring entry points.

Why Build This

Deploy a practical security system to monitor bedroom doors, lockers, or school project storage rooms against unauthorized access or accidental leaving-ajar.

Gain hands-on experience integrating microcontrollers with digital display modules and electromechanical sensors for real-world automation.

Build a portfolio-worthy IoT-style prototype that solves a tangible everyday problem using affordable, modular electronic components.

Real-World Application

Home and office security for monitoring doors, windows, or storage rooms to ensure they are not left ajar for extended periods.

Skills You'll Learn

Microcontroller programming

digital input/output reading

sensor interfacing

time management logic

display driver integration

circuit assembly and wiring

Safety Precautions

Ensure proper wiring of the 9V battery and components to avoid short circuits.

Technology Tags

ARDUINO

ATTINY85

DIGISPARK

TM1637

7-SEGMENT DISPLAY

REED SWITCH

BUZZER

C++

EMBEDDED SYSTEMS

Frequently Asked Questions

How does the microcontroller know if the door is open or closed?

It uses a normally-closed (NC) reed switch and a magnet. When the door shuts, the magnet holds the switch closed. Opening the door separates the magnet, breaking the circuit and signaling the ATtiny85.

Why use a Digispark ATtiny85 board instead of a standard Arduino Uno?

The Digispark ATtiny85 is a compact, cost-effective USB development board that is ideal for small, standalone projects where a full-sized Arduino Uno would be physically too large to fit inside the plastic enclosure.

Can I adjust the length of the countdown timer?

Yes, the countdown duration can be modified within the source code in the Arduino IDE before uploading the program to the Digispark board.

Gallery

This page is part of Kitkraft's Project Hub — a curated collection of electronics & robotics projects gathered from the maker community to help students and hobbyists discover and learn to build. Kitkraft does not claim authorship of the original project, and makes no representation as to the accuracy, completeness or safety of third-party source material. The summary and "How It Works" explanation above are AI-generated, rewritten with reference to the original tutorial — not a reproduction of it. Full credit and a direct link to the original source are provided above. If you're the original creator and have a concern about how your work is represented here, please contact us and we'll address it promptly.

Kitkraft Project Hub — curated from the maker community, credited at the source.

PRJ-00150