A gun case that measures your blood pressure.

There have been many shootings lately, so I was thinking, what if when you own a gun you are required by law to have a special holder that locks the gun inside and prevents it from shooting, then when your heart rate and adrenaline goes up it is detected by the case unlocking the gun allowing you to pull it out and shoot it, of course this would only work when your heart rate and adrenaline gets to a certain point, like if someone was going to kill you with a knife or something.

This can also be used in court to prove that the gun was used for self-defence.

Advantages:
 * Lower risk of using the gun for a wrong purpose.

Disadvantages:
 * The possibilities of using a gun are limited (e.g. can't be used for fun).