Fingerprint door lock on an Arduino Uno

// Fingerprint door lock: an optical fingerprint sensor, a servo latch and a
// traffic light module.
//
//   pins 2, 3      SoftwareSerial: the sensor's TX into 2, its RX from 3
//   pins 12, 11, 10  the light's R, Y and G (resistors on its board)
//   pin 9          the latch servo's signal
//
// The door starts locked and red. A finger on the glass turns the light
// yellow while the sensor searches its library. An enrolled finger turns it
// green and swings the latch open for three seconds; a stranger gets the red
// light blinking. Either way the lock waits for the finger to lift before it
// looks again.

#include <Adafruit_Fingerprint.h>
#include <Servo.h>
#include <SoftwareSerial.h>

const int RED_PIN = 12, YELLOW_PIN = 11, GREEN_PIN = 10;
const int LATCH = 9;
const int LOCKED = 0, OPEN = 90;
const unsigned long OPEN_MS = 3000;

SoftwareSerial sensorSerial(2, 3);
Adafruit_Fingerprint finger(&sensorSerial);
Servo latch;

void lights(bool r, bool y, bool g) {
  digitalWrite(RED_PIN, r ? HIGH : LOW);
  digitalWrite(YELLOW_PIN, y ? HIGH : LOW);
  digitalWrite(GREEN_PIN, g ? HIGH : LOW);
}

void waitForLift() {
  while (finger.getImage() != FINGERPRINT_NOFINGER) delay(50);
}

void setup() {
  Serial.begin(9600);
  pinMode(RED_PIN, OUTPUT);
  pinMode(YELLOW_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
  latch.attach(LATCH);
  latch.write(LOCKED);
  lights(true, false, false);

  finger.begin(57600);
  if (!finger.verifyPassword()) {
    Serial.println("No fingerprint sensor found");
    while (true) {
      lights(true, false, false);
      delay(200);
      lights(false, false, false);
      delay(200);
    }
  }
  finger.getTemplateCount();
  Serial.print("Sensor ready, ");
  Serial.print(finger.templateCount);
  Serial.println(" fingers enrolled");
}

void loop() {
  if (finger.getImage() != FINGERPRINT_OK) {
    delay(50);
    return;
  }
  lights(false, true, false);
  if (finger.image2Tz() != FINGERPRINT_OK) {
    lights(true, false, false);
    waitForLift();
    return;
  }

  if (finger.fingerFastSearch() == FINGERPRINT_OK) {
    Serial.print("Welcome, finger #");
    Serial.println(finger.fingerID);
    lights(false, false, true);
    latch.write(OPEN);
    delay(OPEN_MS);
    latch.write(LOCKED);
    Serial.println("Locked");
  } else {
    Serial.println("Access denied");
    for (int i = 0; i < 3; i++) {
      lights(true, false, false);
      delay(150);
      lights(false, false, false);
      delay(150);
    }
  }
  lights(true, false, false);
  waitForLift();
}