Green’s Dictionary of Slang

knocker n.2

[ety. unknown; ? link to Yid. naches, pleasure]

[late 19C–1900s] (Aus.) common sense.

In phrases

off one’s knocker (adj.)

[1900s] (Aus.) mad, insane, uncontrolled.

put the knocker on (v.)

[2000s] (Aus.) to call a halt, to forbid.