YouTubers test out Ghost Radar, one of the most popular mobile apps for detecting "ghosts." WSJ's Andy Jordan samples the online amateur reviews.

PARIS - Police revealed Tuesday they had infiltrated and taken down an encrypted chat app called Ghost used by criminals ...

For one, you can flip through a selection of Ghost photos and watch a few ... for the tech-minded out there, and the app will also help you find the closest Rolls-Royce dealer.