String code, rs1, rs2, rs3, readString;
void setup() {
    Serial.begin(9600);
    Serial.println("Serial ready!");
}

void loop() {
    if (Serial.available()) {
        while (Serial.available()) {
          delay(10);
          if (Serial.available() >0) {
            char c = Serial.read();
            readString += c;
            rs1 = readString.substring(0, 3); //034
            rs2 = readString.substring(3, 6); //000
            rs2 = readString.substring(6, 9); //017
            code = rs1 + rs2 + rs3;
            Serial.println(code);
            if (code.equals("034000017")) Serial.println("OK");
          }
        }
    }
}