Direct detection of a radio signal or some other EM emission is possible (hence SETI), but given the inverse square law (double the distance, a quarter of the s

Direct detection of a radio signal or some other EM emission is possible (hence SETI), but given the inverse square law (double the distance, a quarter of the signal strength), it's more likely we'd detect a planet with excess oxygen which is believed to be only a by product of life. Also there some fascinating alternatives of biochemistry for life that might work: https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemi... How we detect those is another question.