Using the loop function it should be possible to detect whether a circuit has been broken assuming that the Core has had a digital input and ground wired in series to a circuit.
For take simple circuit consisting only of a battery pack (3v), a light bulb and a switch. If one wires the GND and D1 pin in series to the circuit, it should be possible to detect that the circuit is broken if the switch is pressed. Well, in my head anyway.
Can someone confirm this? Am currently in LAX waiting for a flight so hoping to confirm before I board and not have this going around in my head for the flight to London!