It doesn't appear in the tech tree. But in the crafting menu it's under weapons. It also doesn't have an unlock level listed with it. It's unlocked in my game, I don't know if it just unlocks when you reach a certain level. I'm at 25. I never use it though (did once, drove me nuts every few seconds yelling about "Security Alert", only after I'd already taken out the drone or whatever it decided to yell about), so I never noticed it was unlocked until I went looking to try and help you out. Sorry that wasn't very helpful. I remember seeing it mentioned in the Empyripeda thing, under tricks and tips, though of course I can't find it now that I'm actually looking for it.