Motivation
Modern residential doors are often designed without a traditional external door handle for security and aesthetic reasons, requiring a key for entry. Many of these doors include a simple electric strike operated by a solenoid, but this is usually triggered only via a doorbell intercom system and lacks dedicated control electronics. This approach is often impractical for detached houses or daily use.
The objective of this project was to improve both convenience and security by:
- Integrating a fingerprint sensor directly into the door handle, enabling immediate access after successful authentication.
- Using wireless presence detection via commonly carried devices (e.g. smartphones) to allow recognized users to enter without a fingerprint scan, further reducing access time.
System Design
The system consists of a door handle unit and a basestation that together provide secure and automated access:
- Door Handle Unit: An R503 fingerprint sensor is integrated into the door handle and connected to an Arduino Nano via UART. A spring-loaded door contact is used to transmit the authentication signal and provide a reliable electrical connection, allowing the Arduino to trigger the basestation after successful fingerprint verification.
- Basestation: The basestation is built around an ESP32, which controls the electric strike via a MOSFET. It is integrated into Home Assistant using MQTT for centralized monitoring and control.
- Wireless Presence Detection: A second ESP32 runs the ESPresense firmware and is also connected to Home Assistant. It detects registered BLE devices in proximity and enables automatic door unlocking without biometric interaction.
By combining biometric authentication with wireless presence detection, the system provides fast, convenient, and secure access while remaining fully integrated into the home automation environment.
Control & Measurement
The system monitors authentication events and controls door actuation to ensure reliable and secure operation:
- Fingerprint Processing: Local fingerprint verification is handled by the Arduino Nano, which sends a validated trigger signal to the basestation.
- Door Actuation: The ESP32 drives a MOSFET to reliably actuate the electric strike.
- Wireless Presence Detection: The ESPresense node monitors known BLE devices and triggers door access automatically when detected.
- Integration & Logging: Home Assistant logs all access events via MQTT and allows remote door control.
Fingerprint-based access unlocks the door in under 2 seconds, while wireless presence detection enables unlocking in less than 0.5 seconds, allowing users to effectively walk straight through the door.
Lessons Learned
- Reliable electrical contacts are essential for consistent signal transmission.
- Failsafe design is necessary to maintain usability during network outages.
- Balancing biometric security and user convenience requires careful timing and error handling.