Lots of companies make these, and they’re a lifesaver if you have a two or three-car garage with more than one door. While you might get away with keeping the opener for each door in the car that’s parked there normally, eventually you’ll get caught out wanting to open the other door. You could carry around two separate openers, but why not just pick up a universal that’ll open ’em both?
The pictured remote is made by the aptly-named company Clicker and is sold by SmartHome for $25. There are tons of options, though, so with a little shopping ’round you can easily find one that fits your needs and budget.