Yes, you can detect another person’s consciousness. Christof Koch described a method called ‘zap and zip’. Transcranial magnetic stimulation is the ‘zap’. Brain activity is detected with an EEG and analyzed with a data compression algorithm, which is the ‘zip’. Then the value of the perturbational complexity index (PCI) is calculated. If the PCI is above 0.31 then you are conscious. If the PCI is below 0.31 then you are unconscious. If this link does not work then go to the library and look at the November 2017 issue of Scientific American. It is the cover story.
Zapping the brain with magnetic pulses while measuring its electrical activity is proving to be a reliable way to detect consciousness.