You take a photograph of a card, not seen by your spectator. Your spectator chooses a card from the deck at random. You then send your photo to your Facebook page. Your spectator can then look at your FB page and see the card which they chose.
What you get
An iPhone app on your phone with self contained instructions.
What I think
I'm not a huge fan of phone apps for magic as I think people realise that there is some technology at work but the great benefit of doing this is it gets someone looking at your Facebook page and then you are only a click away from them liking it, which is good for SEO!
I have been trying this with a m***ed deck for added mystery but you could use a Si Stebbins setup instead to get the chosen card.
Yes - several.
A good internet connection is vital which is not always the case so check that it works at your venue before attempting this for real.
Good lighting seems important too, when you take the initial photo. It doesn't always work that well in low lighting.
Do it surrounded? No - you need to hold the key card at arms length to take the initial photo on your phone so this needs to be not seen by any specs I would suggest.
I've had a few tries recently which resulted in a distorted image being sent to Facebook , either completely scrambled or the target card shown but marred by an overimage of a stray club from the original 9S. So not good.
I posted for help on the apps Facebook page and a nice chap asked me if I always held the card in the same way with thumb on the left and three fingers on the right edge. I realised that this might be the answer and switched to holding the card with just my thumb overlapping the card at the bottom. Then I got 3 clean images in a row, even in poor light. So this could be the way forward I think. I hope so as really keen to get this working for my next gig.