someone who can be employed as a detective to collect information

Private Eye is a fortnightly British satirical magazine-newspaper, edited by Ian Hislop.

Private Eye is a video game for the Atari 2600 released by Activision. In it, the player controls French detective Pierre Touche. He drives around an American city in a Model A with the ability to jump up to two stories in the air.

an invisible and easy-to-use PC activity monitoring tool