Anything that can potentially fail when you need it and prevent the gun from firing is not something I want on a defensive firearm. Internal locks on revolvers are an example of this.
A biometric option would be even worse. I've used biometric devices before, and they work so-so. They can be defeated (Mythbusters proved this) and they fail to authenticate the user. Fingerprints, for example, can change over time, due to cuts, abrasions, and warts. I wouldn't want the device to fail to authenticate me when I need it.
The other problem is this: you might need to have a database on each firearm in order for anyone in your household to use it. There are plenty of articles online about families who have a young teen/late tween use the gun in self defense while the parents are out. I can imagine laws would try to prevent that in certain jurisdictions, because some people believe it's better the child get attacked than have to live with the actions of self defense.