You have NO IDEA how effective the finger scanner will be.
Well let's see: if the battery is dead, that effectiveness will be a big fat ZERO.
I'm going to have to charge my gun? What, with a USB cable, or the new QI stuff? How about a Lightning or USB 3.1 port? How about a 120V (or 220V in Europe) plug? Or is it solar?
Are the indicator lights showing the charge, or beeping if it's low (like a smoke detector), or what?
Forget about the very important fact of sensor fingerprint detection ratio (which damn well better be 100.0000% even if it's completely covered in mud or blood), what about the battery and connecting wires? They'd also better able to completely handle water, physical shocks, and mud. IP68 or don't even bother.
Do I need cables to jump start it? Are they Duracell or a no-name brand? Physical package? AAs? 18650? CR123As? WHAT ABOUT BATTERY LEAKAGE from cold or heat? What about adding RAM (EPROM swap actually)? What about the add / delete / change user device reset dance? Or increase sales with single-user device obsolesce: "Sorry, this gun can only be programmed a single time. You can sell it but it won't fire without your finger going with it."
This is NOT a problem looking for a solution. This is stupidly. A gun is a tool -- it fires only when you pull the trigger; it doesn't when you don't. Anything else is a manufacturer defect. That the RIGHT person is pulling the trigger is stupid. If you've had to actually pull a gun you've already lost the battle, best you win the war by shooting. NOW. You only aim at what you want to kill -- otherwise why the hell are you even aiming at it? The ONLY delay should be if you are not aiming at the "right" spot and need to adjust. If you have a backup person, they'd better be able to use it as well. And if you let the wrong person get hold of it ... well you just screwed up badly, didn't you? "Oh, well at least the bad guy can't use it to shoot you." YES he can, he reaches over, grabs your hand and places it on the gun. It unlocks and now everyone's happy again! Well, almost.
Gun Control is being able to Hit your Target.