Pretty basic mod I have been wanting to do for a while. I always leave my car in the garage and if someone picks me up or my girlfriend drives, I have to bring a house key, which I hate doing. I usually just bring my car keys, so being able to to open my garage door with my alarm FOB is very convenient for me.
I will assume this is different for every garage door opener but this is how mine was. I took it apart to first see how it worked. I quickly realized that when I pressed the button all it did was connect to circuits on the motherboard.
Once I realized this I immediately knew what to do. I just needed a relay triggered by an auxiliary output on my alarm.
First step was to "carefully" solder on wires to each of the connecting points.
Next was to wire up the relay. The wires coming from the opener go to points 30 and 87 on the relay. Then 85 goes to a constant 12v source (easy to tap from alarm brain). And 86 to the auxiliary channel of your choice on the brain. I choose channel 4 because on my remote I can change it to say "Garage Door" Instead of channel four.
To test it, just trigger your aux channel and see if the light comes on the opener. It works perfectly for me.
The only issue right now is I will have to take it out to replace the battery. When I get a little bit more free time I will fix this issue by wiring up a 12v source with resistors to match the voltage output of the battery inside the opener.