Green’s Dictionary of Slang

1. a key, esp. a skeleton or duplicate key.

1926		N. Lucas London and its Criminals 241: Here were skeleton keys, or ‘twirlers’ as they were known to crookdom.
1935		R.T. Hopkins Life and Death at the Old Bailey 64: In a burglar’s kit of tools will be found [...] a bunch of skeleton keys, known as ‘twirlers.’.
1956		J. Curtis Look Long Upon a Monkey 96: He’s only collared the twirler in case she’s got up to some villainy inside, without no one knowing.

2. (US black/prison) a prison officer, a turnkey.

1942

D. Burley N.Y. Amsterdam Star-News 21 Mar. 16: ‘One early beam the twirler cam around’.