Sending out Radio Frequency (RF) Signals with Android App

Question

Is it possible to built an app which sends out RF signals? Is it possible to control the exact frequency? So each button would send different frequency signal? How far those signals usually reach?

Answer 1

Yes, but you need some external RF hardware - check out GNU radio and the general subject area of Software Defined Radio.

Answer 2

The app itself will not send RF signal. The app is the logic thay may control a RF hardware.

There are many hardware devices that do this for you.

Arduino could be a simple and cheap solution

to have an idea how a similar project could work look here.