guitar chord
A♯m7♭5
A diminished triad with a minor seventh rather than a diminished one — half diminished, and not the same chord as dim7.
Written the other way round it is B♭m7♭5 — the same twelve keys on a piano, a different piece of notation.
Every fingering that fits a hand
x12120
moderate · barre
676696
moderate · barre
x1212x
moderate · barre
6766xx
moderate · barre
676699
hard · barre
What is true of it
A♯m7♭5 is A♯, C♯, E and G♯ — 1, b3, b5 and b7 counted from A♯.
These are also the notes of C♯m6/A♯ and D♭m6/A♯. Which name is right depends on what is underneath and what came before — the notes alone do not decide.
The easiest of the 5 fingerings below is x12120: 3 fingers, one of them barring the 1st fret, held at the 1st fret.
None of them uses an open string, so this chord moves up the neck unchanged — the same shape 1 fret higher is the chord a semitone above.
1 string stays silent.
Where its notes are on the neck
The brass dots are A♯, the root. Everything else is a chord tone with its degree printed in it.
With a different note underneath
A♯m7♭5/C♯
x46350
A♯m7♭5/E
012120
A♯m7♭5/G♯
4423xx
An inversion is the same chord with a different note lowest. The name changes to a slash name because the bass is what a listener hears as the foundation.