COVID-19 Human to Human 'Proximity' Logger
I once designed a non contact telephone line tracer. The specification was to be able to detect a 1Vpp 1kHz sinusoid signal on a 1 metre length of wire at a distance of 1 metre. The input was a probe tip connected to a static protected FET opamp with a high Q filter. I imagine a 2 metre range could be achieved by pushing the voltage up to about 9V. 

The method I used was essentially an electrostatic pickup. A homemade near field RFID type thing might work as well. Hi Q Coil being fed at (say) 100kHz, with a simply LC being used as pickup. Similar to resonant power transfer.