@cassidy not perfect, but its pretty good (TM). Talking about "pretty good", I strongly recommend reading Signals creator article about PGP called 'PGP and me'. On another note, last time I checked (December), Signal (and by extension [or the other way around]), Whatsapp, have a 'vulnerability' that allows users to pretty much just check if you are using your phone.

https://github.com/gommzystudio/device-activity-tracker