Green’s Dictionary of Slang

paddy n.1

[abbr.]

(UK Und.) a padlock.

[UK]Leaves from Diary of Celebrated Burglar 88/1: Upon reaching the place Joe ‘turned off’ the ‘paddy’.
[US]Number 1500 Life In Sing Sing 258: He sprung the paddy with a screw. He opened the lock with a key.
[US]G. Henderson Keys to Crookdom 413: Paddy. A padlock.
[US]Monteleone Criminal Sl. (rev. edn).
[UK] ‘Screwsman’s Lament’ Encounter n.d. in Norman Norman’s London (1969) 67: We went round to a lockup, to nick ourselves a drag, / We took the paddy off the door, the rest was in the bag.