Colorado-based Biofire Tech is taking orders for a smart gun enabled by facial recognition technology, the latest development in personalised weapons that can be fired only by verified users.

But in a sign of the long, challenging road that smart guns have faced, a prototype twice failed to fire when demonstrated for Reuters this week.

Company founder and chief executive Kai Kloepfer said the software and electronics have been fully tested, and the failure was related to the mechanical gun, which was made from pre-production and prototype parts.