So many great things have been said already!!
I personally like to help give wings to any kind of weird projects, since so many actual innovations come out from side effects of experimentation!!
But in this particular case, there are just SO many pitfalls!!
@Pilgrimsmaster and @Eriequiet have already expertly mentioned most of the core issues with the technical feasibility.
They even already mentioned about legal aspects.
So besides stating that “whilst it is theoretically possible to come up with something that does what you are asking”, the device will look so much different than what you are expecting… to the point that carrying a handheld device is easier and more efficient…
I think the only new things to add here are logical fallacies.
First, the whole purpose behind having it implanted is that it’s hidden and won’t be dropped.
So… being hidden… not the case.
An electric brass knuckle can be hidden. an implant can only be hidden to an extent… I.E. any metal detector or scan will pick that up: good luck ever boarding on an airplane again! Whilst an electric brass knuckle can actually be smuggled into it.
Now… not dropping… Also not the case.
not only because as long as I have a table, chair or a gutter around, I can always stomp it our of your hand.
But malign intent aside, don’t forget that you do want to drop weapons in many valid situations during a fight.
If I am to fight someone with a knife, my main priority is to disarm them.
If you are carrying a knife or a taser, I just need to make you drop it, without harming you too much (else I am in trouble when the police arrives).
But if I cannot make you drop your weapon, then the easiest way to disarm you is by breaking your elbow (which is surprisingly easy to achieve)… And that is also acceptable as a reaction.
So by having it implanted, you are actually only allowing people to fuck you over even more.
Now on a side derail… The non-techy reasons why I think you don’t actually want that implant are the same reasons why I think carrying a knife to a fight is the most imbecile Idea ever:
A knife makes you “win more”, but only if you are already winning. While it makes you “Lose worst” if you are losing.
What does that mean?
If you are fighting someone who’s weaker than you, you will win with or without the knife. So it’s not really a benefit. (All it does is add negative side effects, such as… now You go to jail instead of just getting told off by the police)
If you are fighting someone in your level, drawing a knife does give you an edge (ba-dum-tss), but then you are much more likely to get someone else drawing a gun at you… (I assume you’ve never been in a real-life knife fight before). People who would have let you and your adversary resolve things between yourselves will now intervene if they realise you have a knife/brass knuckles… And you will regret it.
Now, if you fight someone better than you… Having a weapon is the worst thing you can do! Sounds counter intuitive? So bear with me…
If someone comes unarmed against a seasoned fighter, they are seen as a minor nuisance, so they are gonna get a controlled beating. But if they come armed, then they are a risk which must be neutralised (by much more damaging methods)