I also turn on a phantom output when the garage door opens (and turn it off when it closes). Then every minute or so (forgot the interval), announce that the garage door is open if the phantom output is on. Since the garage is an attached garage, the "regular" garage door controller is just outside the door, and I only have a single large door, I don't worry about closing it from an M1G keypad. I also blink a Fkey as long as the door is open. Pressing the Fkey once while the door is open disables the "garage door is open" announcement for some predetermined period of time (30 minutes?). Double pressing it while the door is open turns of the announcement until the door is closed and subsequently opened. The Fkey continues to blink, however, until the door is closed.
Opening the garage door also results in a signal being sent to a wireless relay in my car every two seconds until the door is subsequently closed. If the ignition is on, the relay will cause a buzzer to sound. So I get a "beep, beep, beep" sound in my car if I leave the garage door open, at least until I've driven a few hundred yards from my home.
Lastly, for now, a M1G relay that turns on when the garage door opens (and stays on until the garage door closes or five minutes has elapsed) controls a couple of "parking lasers" in the garage. When the door opens, the laser shines a beam that you can see on the hood of the car. That helps make sure the car is parked correctly, both side to side, and front to back. I dread the day that the parking beam doesn't come on and my wife doesn't stop before she hits the wall...hard. A M1G wireless keyfob in the car can also turn on the laser for five minutes in case the door had already been open for five minutes and the laser had turned off. The keyfob can turn it off, too.