Green’s Dictionary of Slang

erie n.

[SE ear]

In compounds

earysipelas kid (n.) [pun on SE erysipelas, a skin infection]

(S.Afr. Und.) an eavesdropper .

[SA]L.F. Freed Crime in S. Afr. 106: an ‘earysipelas kid’ is an eavesdropper.
erie canal (n.) [pun on SE ear + Erie Canal, a canal in New York State between the Hudson River and Lake Erie]

an eavesdropper.

[US]A.J. Pollock Und. Speaks 36/2: Erie Canal, a person listening in on a private conversation.

In phrases

on the erie (also on the ear-ie)

1. see on the earhole under earhole n.

2. (US Und./prison, also on the earie, …eary) eavesdropping; also used as a warning (see cit. 1949).

[US]Ersine Und. and Prison Sl.
[US]San Quentin Bulletin in L.A. Times 6 May 7: ON THE ERIE, shut up, someone is listening.
[US]D. Runyon ‘A Piece of Pie’ in Runyon on Broadway (1954) 673: Horsey is in there on the old Ear-ie, and very much interested in their conversation.
[US]D. Runyon Runyon à la Carte 25: Around on the Ear-ie finding out what is going on.
[US]Monteleone Criminal Sl. (rev. edn) 166: on the erie [...] a stool pigeon; some one is listening.
[US]Goldin et al. DAUL 65/1: Earie. 1. An eavesdropper. 2. The act of eavesdropping. ‘Zex (look out)! That dude (fellow) on the earie is working too hard (purposefully intent).’.
[US]M. Braly Felony Tank (1962) 15: That sonofabitch was on the Erie!
[US]Ragen & Finston World’s Toughest Prison 798: earie – Listening to another’s conversation; eavesdropping.
[US]R. Campbell Alice in La-La Land (1999) 58: Torino and Hush spent their time on the eary here and there [...] trolling for gossip that could be turned into gold.
[US]R. Campbell Sweet La-La Land (1999) 78: On the eary. Hearing every word that was spoken.
[Can](con. 1920s) O.D. Brooks Legs 69: Too many guys on the eary in here.