As I have chosen the UDP path to control the thingy, I needed a way to send the command datagrams to it. The UDP receive example I used for the arduino, included a processing example for UDP send. After messing around a little bit with processing, I got this:

import hypermedia.net.*;

 UDP udp;  // define the UDP object
boolean overDoorButton = false;
PFont f;


 void setup() {
   udp = new UDP( this, 31337 );  // create a new datagram connection on port 31337
   udp.listen( true );           // and wait for incoming message
   size(220,190);
   f=createFont("Arial",16,true);
 }

 void draw()
 {
   background(10,250,50);
   textFont(f,16);
   fill(0);
   if (overDoorButton == true) {
    fill(200,100);
  }else {
    noFill();
  }
  rect(35, 60, 150, 75);
  text("ABRIR",85,100);
 }

void mousePressed() {
   String ip       = "xx.xx.xx.250";  // the remote IP address
   int port        = 1337;    // the destination port
   if(overDoorButton){
     udp.send("OPEND0123", ip, port );   // the message to send
   }
   
 }
void mouseMoved() { 
  checkButtons(); 
}
  
void mouseDragged() {
  checkButtons(); 
}

void checkButtons() {
  if (mouseX > 35 && mouseX < 185 && mouseY > 60 && mouseY < 135) {
    overDoorButton = true;   
  } else {
    overDoorButton =false;
  }
}

 void receive( byte[] data ) {       // <-- default handler
 //void receive( byte[] data, String ip, int port ) {  // <-- extended handler

 for(int i=0; i < data.length; i++)
 print(char(data[i]));
 println();
 }

To unlock the door, just press the button, and presto! One less excuse to get up and walk.