What camera manufacturer? I am pretty sure any answer will be dependent on the manufacturer as this is a lower level functionality not readily available in generic clients.
I'm sure you mean output, but just for clarification?
This can easily be done with cgi string sent to a camera to arm/enable the input. Like John mentioned it all boils down to whether the camera can handle this and ultimately whether the app has this ability. I work for Mobotix and this can be done with our cameras and the QCamPro app that will run on both iOS and android.
The system is Avigilon, currently there is no way to activate an output from their mobile app.
I would think it possible if the cameras are Profile S (many if not most Avigilon cameras are), since it covers triggering an output.
Though you may have to use something besides Avigilon Mobile (assuming that there is no way there), and possibly open the camera to the internet if ACC cannot be used to pass the command to the camera.