If you're looking for an app to scare your friends, you should check out Sweep Ghost Box by ChillSeekers. Considered a Trans Communication (ITC) application, Sweep Ghost Box allows users to engage in spirit communication. It features a sweep rate and seven audio channels. Additionally, it includes audio effects as well as a forward and reverse audio sweep function. 

Sweep Ghost Box also offers pre-installed audio files to aid you in your ghost-hunting endeavors.  Sweep Ghost Box is compatible with devices with Android 4.1 and newer. You don't need to pay because Sweep Ghost Box is free to download on the Play Store.