Green’s Dictionary of Slang

alert to, aware of, ‘fly’.

1789		Merry Fellow’s Companion 28: ‘Stagging, my lord;why you see, was down upon him’.
1802		M. & R. Lovell Edgeworth Essays on Irish Bulls 138: ‘Up to him!’ says his lordship, ‘what do you mean by being up to him?’ ‘Mean, my lord! why, I was down upon him’.
1812		Egan Boxiana I 4: They are not down to the ‘Sublime and Beautiful’ or up to the ‘Diversions of Purley’.
1821		‘An Amateur’ Real Life in London I 63: No man was better up to the rigs of the town; no one better down to the manoeuvres of the flats, and sharps.
1844		New Sprees of London 3: Nanty palary the rumcull of the Casey is [...] quisby in the nut, not fly, not up to the moves, not down to the dodges, not awake, can't tumble to the slums, not wido to the slangs.
1848		Bell’s Life in Sydney 26 Aug. 1/2: [N]ot being what the young scapegrace Rugbinian would call ‘down,’ or rather, ‘up’ to his slang.
1850		F.E. Smedley Frank Fairlegh (1878) 40: Ya’as, you’re about right there, Mr. Lawless; you’re down to every move, I see, as usual.
1874		M. Clarke Term of His Natural Life (1897) 248: I know these fellows [...] I’m down to all their moves.
1885		Bulletin (Sydney) 2 May 23/1: In order to burst the thing up at once, we sternly tell the people who are advertising for ‘dry, airy cellars,’ that we’re down to what they’re up to.
1890		‘Rolf Boldrewood’ Colonial Reformer III 86: I saw the old boy was down to every move I had made. Knowing old shot, too, in spite of his politeness and humbug.
1903		A.H. Lewis Boss 122: He’s old-fashioned [...] he aint down to date.
1926		K.S. Prichard Working Bullocks 82: Peter’s down to it, Red.