In the picture is the PCB from the inside of a traditional garage door opener is laid on top of the ethernet shield + arduino uno combo. The transistor is pushed into the heated solder points of the push button with the center pin going through a 10k resistor to the output pin of your choice.
This 2nd example in this tutorial for lighting an LED can be copied without editing to use pin 2. The tutorial also walks you through testing the local address that will trigger the button. Now you can create a shortcut or bookmark to the website on your smartphone to be able to open with one click.
While this is all you need, I've also soldered wire to replace the battery. Since this one uses a 3v battery it's going to the 3.3v and ground pins on the board.
Adding to it by opening with a text
So in the rare occurance that I'd need to open the door while away (family member locked out of the house.. just takes one time). I decided to go with sending a text. For the time being I have an older android phone as a "home phone" and this script should be easy to replace the check for new texts section with anything from checking email to checking twitter and can easily grow into a smart home station. Aside from the wifi setup as the foundation, this involved downloading the SL4A app from here. Then create a Python script with the following code:
droid = android.Android()
var = 1
while (var == 1):
smscheck = droid.smsGetMessages(True, 'inbox')
for i in smscheck.result:
if 'Open Sesame' in i['body']: # The command you want to send via text
url = '192.168.1.xxx' # IP address of ethernet shield goes here
uri = '/?2' # Pin number being used should replace 2
ES = httplib.HTTPConnection(url)
ESreply = ES.getresponse()