How to use sensors for my overhead garage doors

I have been thinking the same thing. If mounted on either side, the sensor would likely come off when the door is fully up. I know some alarm companies have special garage door sensors advertised, but I don't know how they are different. Seems like an opportunity for SimpliSafe. I have another opportunity, but this one may not be nearly as popular: a mailbox sensor for the curbside mailboxes to indicate when they have been opened. Not necessarily an "alarm," but this way you know if the mail has come or not on bad weather days. It would need to function farther away and work well in cold weather (maybe with a solar option like the cameras). Should not cost as much as the cameras! ;-) 

I have mine working fine.  See photo.  I have mine set to Secret Alert in all modes.  When we go on a trip, I change Away to Alarm.  

What I did was position each side of the sensor with duct tape to test various setups.  I used the door on manual mode, i.e. disengaged the opener, so I could SLOWLY raise it up and down.  It took a few tries to get it right.  Basically, the small side sits on the top rail, and the bigger sensor is on the wall, and they pass each other as the door arcs away from the wall. 

I installed one yesterday based on a youtube video.  It utilizes a bendable metal strap to move the sensor a few inches away from the door.  It was trial and error to get the right position and clearance but it works.  The videos show use of a galvanized framing tie but I used an aluminum gutter down spout strap.

Google " simplisafe entry sensor - garage door installation " and you should be able to pull up the same one I went by.

Depending on the age of your house and what type of security system already existed, you might already have some sensors on the garage doors that hook into an old alarm panel. If you do, go to the panel and locate the garage door wires using a continuity checker/ohmmeter and solder them to either side of the reed switch inside one of the regular door sensors.

I'm not saying this is exactly what I did for my grandparents' house and that it's been working well... Good luck!

Etsy seller. Simplisafe garage door bracket. It's $4. I used two and put two 3M adhesive strips on them. Holds fine on that metal strip on the side of the garage door. I personally used teh aqara sensor model, but that's another story.

https://www.etsy.com/listing/881058837/garage-door-bracket-for-current