What could go wrong if you made a circuit-breaker-tripper with its own circuit breaker?
In theory, that sounds great.  In reality, maybe not so much.  You could be talking about putting a crap-ton of current through the house wiring, and a device in your hand!

Looking at a 20 ampere circuit, where the receptacle is 20' (along the wire) away from the breaker. That's 40' of wire in the wall.  According to NEC, 12 AWG wire has a resistance of 0.00193 ohms per foot. Assuming the wiring for the device is 12 AWG, and about a foot in length.  That's a total of 41' of wire, at 0.00193 ohms per foot. 

Using Ohm's Law, we can calculate the fault current.

I = V/R
I = 120 v / 0.07913 ohms
I = 1,516.492 amperes

That's more than 75 times the rated current of the 20 ampere breaker, so it should be within the instantaneous trip range of the breaker.  If the house breaker does not open, you've got 1500 amperes flowing through the house wiring, and a device in your hand. Hopefully the breaker in your device works, and opens the circuit in less than a cycle.  Otherwise, that wire is going to get really hot, really fast.