It’s getting easier to watch the watchers:

A teen suspect’s snap decision to secretly record his interrogation with an MP3 player has resulted in a perjury case against a veteran detective and a plea deal for the teen.

Unaware of the recording, Detective Christopher Perino insisted under oath at a trial in April that suspect Erik Crespo wasn’t questioned about a shooting in the Bronx.

But the defense confronted the detective with a transcript it said proved he had spent more than an hour unsuccessfully trying to persuade Crespo to confess.

Perino was arraigned today on 12 counts of first-degree perjury and freed on bail.