You don’t typically see guns at San Francisco tech confabs. The city itself saw its last gun store close in 2015. But on a sunny February morning, a ballroom at the Palace Hotel is filled with an unusual mix of engineers, veteran police officers, dot-com investors and gunsmiths. Some of them—mostly cops—are visibly packing.

We’re gathered for the 2016 International San Francisco Smart Gun Symposium, billed as a response to President Obama’s January remarks on gun safety. After citing gun accident statistics, Obama asked: “If...