Possibly to go to the shooting range, or to your job as a security guard? Or, in the cases of less conspicuous ghost guns than the AK-47 purportedly involved in this case, to carry on you for self-defense? All of these are common and legal in the US in general, whatever I may think about their ethical implications.

Interesting that it is ok in the US. I also work in weapon detection for driver safety systems. Obviously it is impossible for a human or a machine to detect intent with accuracy. A security guard can enter the car and then shoot the driver. You never know. That is why our systems always send alerts no matter the situation.