Short answer: most garage door openers made in the last several years already come with battery backup built in, and whether you specifically need it has less to do with a strict local law and more to do with whether you're okay being locked out of your garage the next time the power drops during a dust storm. If your spouse says it's 'just a gimmick,' they're half right — it's a convenience feature for most households, but it can be a real requirement if your garage door is the only way in or out of the garage and the garage has no separate door to the outside.