Since I hadn't seen anyone post anything like this, here is what I did to get my simple Lift Master Garage Door opener to trigger off me flashing my High Beams as I approach. I really didn't want to wire another switch on my bike, and didn't want to make any permanent changes to my controls/handle bars. I wanted something stock looking and hopefully using something already existing. I suddenly thought, "Hey, why not just use my already existing Hi Beam switch". But you don't want that sending a continuous broad cast of the door opener, so just a quick pulse when you first turn the high beams on to trigger the door opener was what I wanted. Got my trusty HP-48c calculator out and targeted the pulse time I wanted, and how much steady state current I was fine with it using (when Hi Beam is on).
Just crack open your existing door opener remote and rip out the PCB guts of it if you have an available spare, OR go buy a $10 compatible one for your door opener. Make sure it is 3.3v based, and most of these are "triggered high". I could probably show you how a GND trigger could work too, but this represents the bulk of the door openers I've seen (I used Lift Master). If your garage opener is a learning one, it should work with pretty much any door opener remote.
Here is an example of it working
Hopefully, it helps some of you if you have even a little soldering knowledge. I love this. I wrap it in a sealed sandwich baggie, and just tape it inside the cowling or head light housing, and it has pretty good range (150 yards away). I could have designed one that took power supply too, but I didn't want a 3-wire install, and you don't always have a constant 3v source. So, this just requires the original 3.3v door opener battery, and you will have to change it out, like every 5 years, but that is easy. I used the head light plug as my tap point on the HIGH BEAM side, just because that felt like the ideal point. Essentially, every time you engage the hi beam, it will create a short 2 second pulse on the garage door opener for a 3v signal to trigger it to operate. If you leave the hi beam on, no worries, it is only drawing 0.1mA while on and not producing any more pulses (nearly 0v). Make sure your garage door opener is 3.3v based, and triggered hi (you can tell, by measuring the voltage on both sides of the small momentary push button on the opener. One will be GND and the other side will be 3.3v when open. Which ever side changes (it should be the GND side) when you push the button is what you solder the diode output to and then connect any other TRUE ground side of the PCB (hopefully coming right off the small watch battery holder) to the middle of the two 10k resistors. Wire up a connector (I used RC plane extension servo leads) to your head light, and you are good to go. I will assume you've already "bound" the door opener to your garage door before doing this.
Just to be clear, you are ONLY making the pulse circuit in the center. The part on the left and right is just to show you what basically already exists (motorcycle head light on left and Garage remote PCB on right). Connect to it however you like but there are 2 inputs (motorcycle ground and the 12v hi beam tap) and 2 outputs (remote switch side and remote ground) to the circuit. Note, you are NOT shorting motorcycle GND to PCB ground!!!
This burns NO current when HI beam is off or when bike is off (even with high beam switch on) and there is only normal standby current demand on the remote battery (very very very small). While the bike IS running and Hi Beam is ON, it will burn about 0.6mA from your bike to begin with, but within 2 seconds, that will dissipate to <0.1mA. Essentially next to nothing compared to your head light. Originally, on my implementation, I didn't have the 20k output current limiting resistor or the 3.3v zenner diode, which without, yes, it produces a short time that is a little over 4.5v on the PCB remote input. Put them in, if you like. I didn't bother and it should not burn out the remote opener chip/battery. Also, the PCB diagram is just a quickie representational diagram to give you a good idea what to connect to...
I take NO RESPONSIBILITY for you damaging your opener or bike...this is reference only and like most DIY, at your own risk!!!