Hi, you can do everything you imagine.
For example the Logout:
See code for login (https://forum.nfcring.com/topic/392/logging-into-desktop-with-arduino/3).
Replace the code "Keyboard.println("password");" at the end with the following code:

Keyboard.press(KEY_LEFT_GUI);
Keyboard.press('l');
delay(100);
Keyboard.releaseAll();

This code presses the Window Key and the "L" key at the same time, so your windows computer will be locked.
For more information, read the Arduino docs: http://arduino.cc/en/Reference/MouseKeyboard
You can emulate the Keyboard and the Mouse with an Ardunio Leonardo

it works both.
Connect it to 5v if it says in the manual.

Yeah - interesting idea - i will tinker with the code in my next spare time to improve the code.

@Lokki what are your error messages in the arduino ide?
@Nairod785 here are some pictures:

You want to Login to your Desktop with your NFC Ring?
You have an Arduino Leonardo, an NFC Ring and an Elechouse PN532 reader (v3 recommended)?

Great, lets build a Log-In Station for your Laptop.
It works with nearly every password field (Debian Linux Login, Windows 8.1 Login, Keepass tested and worked - BIOS password doesn't work).

Connect the Elechouse reader to the Arduino Leonardo (see below) and connect the Arduino via USB to your computer.

PN532 Module <-> Arduino

GND <-> GND
VCC <-> 3v3
SDA <-> SDA (on Arduino Leonardo D2)
SCL <-> SCL (on Arduino Leonardo D3)

So here's the code:

#include <EEPROM.h>

/**************************************************************************/
/*!
Autor: Pascal König
Website: http://blog.koenig-pascal.de

Elechouse NFC Module v2.0
Library: https://github.com/elechouse/PN532
NFC Code Template: https://github.com/JohnMcLear/NFC_Ring_Arduino_Door_Lock/blob/master/NFC_Door_Lock.ino

*/
/**************************************************************************/


#include <Wire.h>
#include <PN532_I2C.h>
#include <PN532.h>

PN532_I2C pn532i2c(Wire);
PN532 nfc(pn532i2c);


void setup(void) {
  Keyboard.begin();
  Serial.begin(115200);
  Serial.println("Hello!");

  nfc.begin();

  uint32_t versiondata = nfc.getFirmwareVersion();
  if (! versiondata) {
    Serial.print(versiondata);
    Serial.print("Didn't find PN53x board");
    while (1); // halt
  }
  
  // Got ok data, print it out!
  Serial.print("Found chip PN5"); Serial.println((versiondata>>24) & 0xFF, HEX);
  Serial.print("Firmware ver. "); Serial.print((versiondata>>16) & 0xFF, DEC);
  Serial.print('.'); Serial.println((versiondata>>8) & 0xFF, DEC);
  
  // Set the max number of retry attempts to read from a card
  // This prevents us from waiting forever for a card, which is
  // the default behaviour of the PN532.
  nfc.setPassiveActivationRetries(0xFF);
  
  // configure board to read RFID tags
  nfc.SAMConfig();
    
  Serial.println("Waiting for an ISO14443A card");
}

void loop(void) {
  String ringUid;
  boolean success;
  uint8_t uid[] = { 0, 0, 0, 0, 0, 0, 0 }; // Buffer to store the returned UID
  uint8_t uidLength; // Length of the UID (4 or 7 bytes depending on ISO14443A card type)
  
  // Wait for an ISO14443A type cards (Mifare, etc.). When one is found
  // 'uid' will be populated with the UID, and uidLength will indicate
  // if the uid is 4 bytes (Mifare Classic) or 7 bytes (Mifare Ultralight)
  success = nfc.readPassiveTargetID(PN532_MIFARE_ISO14443A, &uid[0], &uidLength);
  
  if (success) {
    // Display some basic information about the card
    // Serial.println("Found an ISO14443A card");
    // Serial.print(" UID Length: "); Serial.print(uidLength, DEC); Serial.println(" bytes");
    Serial.print(" UID Value: ");
    for (uint8_t i = 0; i < uidLength; i++)
    {
      //Serial.print("..");
      //Serial.print(uid[i], HEX);
      ringUid += String(uid[i], HEX);

    }
    //Serial.println(ringUid + "\n");
    Serial.println(ringUid);
    if(ringUid == "publicRingUID"){
      Serial.println("public");
    }
    else if (ringUid == "privateRingUID"){
      Serial.println("private");
      Keyboard.println("password");
      delay(5000);
    }
  }
}

Change your password at the end of the code (in the private Ring Area).

And here's a video

If you have questions: Feel free to ask.

should be no problem with an arduino leonardo (or similar) and an elechouse nfc reader.
In my next free time - i will try this.

Here are more Pictures:

Do you want pictures of anything in particular?

Now, here we go:

Short Description:

Connect the PN532 Module as follows:

PN532 Module <-> Arduino

GND <-> GND
VCC <-> 3v3
SDA <-> SDA (on Arduino Uno A4)
SCL <-> SCL (on Arduino Uno A5)

For TWI Pins of other Boards, see Arduino Boards Page

Connect the 433Mhz Transmitter as follows:

433Mhz Transmitter <-> Arduino

DATA <-> Data Pin (i use Pin 10)
VCC <-> 3v3
GND <-> GND

Do you have any questions? Feel free to ask!

Hi @Lokki thanks - I already ordered an Elechouse V3 Reader, but till it arrives i build the prototype with my v2 reader.

So here's an Image:

The parts list:

• An Arduino
• Elechouse PN532 reader (V3 recommended - see @Lokki comment
• 433Mhz Transmitter (e.g. from eBay)
• a working outlet device (see here)

And the source code:

#include <EEPROM.h>

/**************************************************************************/
/*!
Autor: Pascal König
Website: http://blog.koenig-pascal.de

Elechouse NFC Module v2.0
Library: https://github.com/elechouse/PN532
NFC Code Template: https://github.com/JohnMcLear/NFC_Ring_Arduino_Door_Lock/blob/master/NFC_Door_Lock.ino

RCSwitch Library: https://code.google.com/p/rc-switch/

*/
/**************************************************************************/

#include <RCSwitch.h>

RCSwitch mySwitch = RCSwitch();


#include <Wire.h>
#include <PN532_I2C.h>
#include <PN532.h>

PN532_I2C pn532i2c(Wire);
PN532 nfc(pn532i2c);


void setup(void) {
  mySwitch.enableTransmit(10);

  Serial.begin(115200);
  Serial.println("Hello!");

  nfc.begin();

  uint32_t versiondata = nfc.getFirmwareVersion();
  if (! versiondata) {
    Serial.print(versiondata);
    Serial.print("Didn't find PN53x board");
    while (1); // halt
  }
  
  // Got ok data, print it out!
  Serial.print("Found chip PN5"); Serial.println((versiondata>>24) & 0xFF, HEX);
  Serial.print("Firmware ver. "); Serial.print((versiondata>>16) & 0xFF, DEC);
  Serial.print('.'); Serial.println((versiondata>>8) & 0xFF, DEC);
  
  // Set the max number of retry attempts to read from a card
  // This prevents us from waiting forever for a card, which is
  // the default behaviour of the PN532.
  nfc.setPassiveActivationRetries(0xFF);
  
  // configure board to read RFID tags
  nfc.SAMConfig();
    
  Serial.println("Waiting for an ISO14443A card");
}

void loop(void) {
  String ringUid;
  boolean success;
  uint8_t uid[] = { 0, 0, 0, 0, 0, 0, 0 }; // Buffer to store the returned UID
  uint8_t uidLength; // Length of the UID (4 or 7 bytes depending on ISO14443A card type)
  
  // Wait for an ISO14443A type cards (Mifare, etc.). When one is found
  // 'uid' will be populated with the UID, and uidLength will indicate
  // if the uid is 4 bytes (Mifare Classic) or 7 bytes (Mifare Ultralight)
  success = nfc.readPassiveTargetID(PN532_MIFARE_ISO14443A, &uid[0], &uidLength);
  
  if (success) {
    // Display some basic information about the card
    // Serial.println("Found an ISO14443A card");
    // Serial.print(" UID Length: "); Serial.print(uidLength, DEC); Serial.println(" bytes");
    Serial.print(" UID Value: ");
    for (uint8_t i = 0; i < uidLength; i++)
    {
      //Serial.print("..");
      //Serial.print(uid[i], HEX);
      ringUid += String(uid[i], HEX);

    }
    //Serial.println(ringUid + "\n");
    Serial.println(ringUid);
    if(ringUid == "YourFrontRingUID"){
      Serial.println("public");
      mySwitch.switchOn("11111", 1);
    }
    else if (ringUid == "YourBackRingUID"){
      Serial.println("private");
      mySwitch.switchOff("11111", 1);
    }
  }
}

The schematics, an arduino diagram and a little howto is following.

So here's a video of my prototype for a light switch with Arduino.
Code, Tutorial and Images are following.
https://mediacru.sh/uuF-Ulrhdwey