Edward Snowden's New Research Aims to Keep Smartphones from Betraying Owners
No disrespect to Snowden and Bunnie, but it seems to me that a much simpler solution giving you a much higher OPSEC is to buy a smartphone with a removable battery. No battery, no radios are on.And if you are truly paranoid, it's simple to disassemble the phone and look for/remove any backup batteries. I know, I had to pull the backup battery from my wife's Moto G after it fell in the sink.