one-two checker, n. — Green’s Dictionary of Slang

one-two checker n.

[the trad. one-two, one-two used to check a microphone or PA system]

(rap music) a cautious person, one who assesses a given situation.

2003

Wreckx-N-Effect ‘Rump Shakes’ 🎵 Yup yup it’s Teddy, ready with the one-two checker. / Wreckx-N-Effect is in effects but I’m the wrecker / of the track.