Which preposition to use with eavesdrop

at Occurrences 3%

One needn't eavesdrop at the key-hole with this little instrument about.

on Occurrences 2%

Everybody seems eavesdropping on everybody else.

in Occurrences 1%

It was all very like the conventional stage picture of Western melodrama: the fire lighting up their faces with patches of alternate red and black; Défago, in slouch hat and moccasins in the part of the "badlands" villain; Hank, open-faced and hatless, with that reckless fling of his shoulders, the honest and deceived hero; and old Punk, eavesdropping in the background, supplying the atmosphere of mystery.

with Occurrences 1%

When he had rung the bell, she leaned back; in her chair and eavesdropped with sparkling eyes.

Which preposition to use with  eavesdrop