https://www.vox.com/the-goods/2018/10/5/17942874/ghost-hunting-apps-tools-halloween-october
According to a paranormal investigator and software engineer:
EMF meter
K2
IR Lights
Spirit Box (she recommends the SonoX10 app, or SonoX12 for android)
She does not like the ovilus or any of the Ghost Radar type apps.