Install a simple indicator which will alert you if you've left the garage door open. Total cost is less than $30-$40, and you can determine exactly where the indicator will be located.
What you'll need:
-A 24 volt doorbell transformer
-1 push button "normally open/momentarily closed" switch
-1 red LED - 2.8 volts
-1 4.7k-Ohm resistor (specific part numbers for the electrical components are provided in Step 2)
-2 strand bell wire
-Electrical tape and/or heat shrink tubing
-Soldering iron + solder
-Misc. hand tools - wrenches, etc. - depending upon the specifics of your installation
Let's get started...
Step 1: Identify a switch location
When I looked at my garage door, I noticed that a piece of galvanized trim on the top of the door stopped right next to the angle iron used to hang the door tracks when the door was in the fully opened position.
I bought a simple corner or "L" bracket and mounted it from the bolt that connected the wheel track of the door to the vertical angle iron bracket. A simple Radio Shack "normally open/momentary close" push button then mounted on the other side of the corner bracket, with the switch of course facing the top of the door.
By bending the bracket slightly, I was able to ensure that the switch was fully depressed every time the door was fully opened.
This arrangement might work for you, or you might have to improvise a bit. You of course want to mount the switch in a manner that it's in the "closed" position when the door is open.
NOTE: in the image below, I stopped the door's movement before it reached the fully open position so you could see the orientation of the switch in relation to the top of the door. When the door is fully open, the red push button is fully depressed, and the circuit is closed. (See 2nd picture below.)