This method lets you open the door from anywhere — whether you're home or not, and watch a live feed from your garage on your phone. It's perfect for letting the kids in when they get home, or just checking to see if everything is ok. Instructables user zarkani made this home security project a reality, using an old Android phone, some easily-available electronics and a free Android app called Alfred Security IP Cam. In short, he sets up the old phone in his garage, actually connected to your garage door opener directly using a photocell. When it's not opening or closing the garage door, it acts as a security camera you can watch from anywhere on the web (provided you set up your home network to allow you access remotely) and when you need to open or close the garage door, just use the app to activate the garage phone's flashlight — that will trip the photocell and open the door.
The whole process is fairly simple, and outlined in the video above. At the Instructables link below, he gives you the circuit diagram you'll need to build the light-activated control for the door opener, although he leaves it to you to wire up the circuit to your specific garage door model. Make sure to check the comments of the Instructable too — he links to where he got all of the parts and some more clarifying details down there.
Open Your Garage Door from Anywhere Plus Security Cam! [Instructables]