Tech Arcanist

Multi Tier Secure Lock System

The Multi-Tier Secure Lock System is an advanced secure door locking solution built using an ESP32, integrating multiple authentication layers used in enterprise access control systems: Passcode → RFID → Fingerprint → Email OTP (Gmail) → Google Authenticator OTP. This multi-stage authentication prevents unauthorized access even if someone knows one credential, ensuring maximum security and eliminating single-point vulnerability.

Features

  • Solenoid Door Lock Mechanism
    • Unlocks only when all authentication stages are completed successfully.
  • 5-Tier Authentication Sequence
    • Passcode input (keypad)
    • RFID tag authentication
    • Fingerprint biometric verification
    • Email OTP — OTP is sent via Gmail to the registered Gmail
    • Google Authenticator Time-Based OTP (TOTP)
  • Admin Mode
    • Special bypass mode with admin passcode + admin fingerprint
    • Ability to add/register new fingerprints
  • User Mode (Layered)
    • Complete verification sequence enforced

Components Used

  • ESP32 — Microcontroller handling entire authentication logic
  • Solenoid Lock + Relay — Door locking mechanism
  • Keypad — Passcode input
  • RFID Reader Module — Layer 2 authentication
  • Fingerprint Sensor — Biometric scan
  • Buzzer — Status alerts / feedback
  • OLED — Shows verification progress
  • Wi-Fi + Gmail SMTP — Sends OTP via email
  • Google Authenticator API (TOTP) — Final authentication layer

How it Works

  • User enters passcode → If correct, move to RFID
  • User scans RFID card/tag
  • User gives fingerprint scan
  • ESP32 generates an OTP and sends it via Gmail
  • (Email → Gmail inbox of authorized user)
  • User enters Google Authenticator TOTP
  • If all layers verified → Relay activates solenoid → Door unlocks
  • If any layer fails → System resets → Access denied
  • Gmail OTP + Google Authenticator TOTP makes the system resistant to brute-force attacks.

Media Availability (Important Note)

This project was built a long time ago.
There are very limited photos/videos of the working system

Working

Old working Clip1 (Insta Story)

Old working Clip2 (Insta Story)

Old working Clip3 (Github)

Circuit

Circuit Diagram

Code & Installation

The complete source code is available in the GitHub repository.
View on Github –>

My Learnings

  • Integrating multiple authentication modules into a single access control system
  • Implementing Gmail SMTP email OTP sending directly from ESP32
  • Using Google Authenticator TOTP with secret key handling
  • Working with secured credentials and preventing exposure in code
  • Designing a multi-stage state machine that controls the authentication flow
  • Managing relay-driven solenoid lock circuits while maintaining electrical isolation
  • Admin privilege system: bypass authentication + add new fingerprints