I am using an emonTH to monitor domestic hot water temperature. I now want to add monitoring the Thermostat switch operating. I can separate the cores to and from the thermostat. Is there a non contact way of monitoring the wire from the thermostat such that it can signal a digital input. High when voltage present, low when no voltage present. Ideally battery powered. At worst I could put in a mains relay that is tricky as there appears to be no neutral in the wiring. I am guessing it is very low current.