Green’s Dictionary of Slang

aware of what is going on, at one with the nuances and niceties of a situation or conversation.

1959		F. Norman in Encounter n.d. in Norman’s London (1969) 63: I dig, man, my chick’s real tuned in to that kick, every time I see her she’s doing a flip, but she’s never got enough bread to give the pusher.
1968		L. Wolf Voices from the Love Generation 11: The Dead, the Holding Company, the Airplane, all these people are tuned in.
1978		R. De Christoforo Grease 207: Someone like me, who is basically tuned-in.
1987		J. Jerome q. in Firestone Swing, Swing, Swing (1993) 238: ‘Benny always seemed able to get good players who could do the gig. There were so many musicians like myself who were already tuned into the band’.
1999		K. Sampson Powder 340: She was sharp and focused and tuned in to the minutiae.