Re: The user replied: "The same electrician who changed that plug rewired my house last week!"
The device you describe in your post is an RCD - Residual Current Detector. This identifies the amount of current going "missing" from the circuit (the live and the neutral) and when this exceeds a set amount it will interrupt the supply. (typical values for residual current are 10mA, 30mA and 100mA for large equipment)
A GFI type device relies on the current flowing through the ground circuit through it to detect the issue and interrupt the circuit. The drawback with these is that if the current flows to ground through an alternate path (eg. a person), the GFI will not detect this and interrupt the circuit.