SD shooting is going to require you to process some information - is that guy armed with a gun or just a cell phone? Is that a burglar or my teenager sneaking in?
Couple of simple things I do with my iPhone; I have "Coin Flip" and "Pretty Random" Apps on my phone. If you want to work with two targets at a time, use coin flip and assign one target heads and one tails. If you are using your six circle target, use the random generator app and limit the range of possible numbers. You could limit to 1-6, or even 1-7 or 8 - the numbers that don't have a circle associated become "don't shoot" numbers. Mix up label sequence from visit to visit so you have to think a little more.
I like to shoot with a larger "high center chest" target; maybe 8" circle, 8" x 8" square, or simply a sheet of paper folder in half. I limit the random generator to 1-9. The high center chest target is for any odd number. I draw four other smaller shapes and number them 2, 4, 6, and 8. I make each of those shapes different in size/shape so I have to balance how fast I can shoot vs. precision needed to hit. Even numbers get enough shots for one hit, odd numbers require a random number of shots usually between 2 and 5 (I'm in Cali so stuck with 10 round mags) in a string of fire as fast as I can keep them in the box. Of course, varying the distance of the target changes the speed and precision for all the shapes.
To be safe, I put the phone out in front of me, hit the button and assume a high or low ready. When I'm set I look down at the screen and figure out what I'm supposed to shoot. That way I'm not fumbling around with a phone and gun at the same time, which would probably drive your RSO bananas.