You can read more about it
here at Honda's page. It uses four crash sensors on the front fork to monitor acceleration changes, and a central ECU to determine if the airbag is needed.
False triggerings would be awful, of course, and put Honda wide open for lawsuits. I'd guess they've spent a lot of time and money to avoid that scenario.
Besides Honda, there are also a number of vendors, such as Hit-Air, that have developed airbag jackets and vests.
Hit-Air