That's just a scope. Comes right off and the gun reverts to a regular M4.

Most(though not all) other smart gun attempts work in a similar fashion; the host gun works exactly as it were, except an extraneous metal bit inhibits firing. If the bit was removed or held down, it reverts to the original host gun and fires normally. As such, the extra bit is literally extraneous, irrelevant to the gun's working.