Basically I need to build an APP to communicate between two android devices, send and receive data, in the safest way without Internet.
I could use WiFi, but they are prone to hacks and Jamming. My first question is if Local WiFi Hot Spot connection could be made fully secured to public?
I am looking into wired communication between android devices using OTG USB serial communication. My second question is Are there ways to communicate between android devices over OTG-USB using serial ports?
As Android supports both USB gadget and USB host interface, it is definitely possible to make communication between two devices over USB OTG. In this case, your one device will become USB Host which will initiate connection. And the other will become USB gadget device. And you will have to write application considering that.