I found a safe distance is about 10 feet or so which I believe is a good enough distance as it doesn't challenge the audience's attention too much. But when I perform it I use the idea of performing it under test conditions. So I have one person (who will check the stuff later) check my ears and such to make sure I do not have any communication devices. I take off my smartwatch and put it in my case. I then invite the participant on stage and explain what is about to happen. I tell them to keep it fair I will make some make-shift boards out of 2 pieces of kitchen cutting boards, some bulldog clips, and paper. I show both sides of both boards. My left-hand covers the device. I show the backs and without drawing attention to it, I rotate my hands inwards. This showing the backs without telling the audience. I then build the clipboards in front of everyone. This gives them reassurance that they are just what they say they are and causes no alarm of suspicion. The issue I do have tho is with the peek. It's a bit hard to peek sometimes. As I posted in my review on Vanishing, This device is worth its price if you can afford it. There are more expensive versions out there for sure that are more reliable, operate better. But then there are the cheaper versions with more analog methods that also work well. THis is a nice middle ground. But I also make sure I have a backup just in case it does not work. (Back up meaning another effect I can turn it into if the devices fail)