I am doing just this. I use the SmartThings multi sensor on the door. No need to put the ‘magnet’ side of it, just the sensor itself. It knows orientation/tilt/motion. It also does temp which is cool. Battery life so far, well I’m on the battery it came with and I’m at 8 months or so with it. It got down to like the teen’s outside here, inside the garage I have it alerting for below 42 which it did a few times. Battery has been fine.
I get a push notification everytime the garage door is opened or closed. It also works in the smart home monitor as a ‘door’. Im not sure of the magic, but I named it garage door so not sure if that had anything to do with it or what. But it seems to ‘just work’. Its not the cheapest but its one of the sensors I have had the fewest issues with. Every now and then, like 4 times since I installed it, ive had to hit refresh a few times or smack it to get it to realize it was ‘closed’. It knows vertical orientation vrs horizontal for what is closed v open.