I'm going to do a routine where I read someone's mind and unlock their phone. I have them write down their PIN beforehand in case we need to verify it afterwards (ahem), but I wonder about trusting someone to write down their real PIN.

I'd hate to get to the last digit, tap it in and have the phone not unlock. If that happens I can write down the numbers I received and have someone else read out the numbers that were written down to prove I received the numbers the participant was focused on. But that's kind of a bummer ending.

I'm wondering about having a 3rd party take the phone and written number and verify it works before reading the participant's mind, but that feels awkward. And slow. A break in the action.

Should I just trust they'll be truthful, but have the "write it on a big pad" reveal in my back pocket just in case?

Jay

Pm me and I will tell you how I cover off exactly this possibility. As this is a public forum I can't go into details here.

Mark

Ask your participant to change their pin code, so he/she won't have to use their "real" pin code.
Ask them to write this new pin code down in case they forget it (ahem)

Tell them to change their code to the original one when you are finished. That way they don't feel threatened.

Of course, assuming the dirty works is done before the show. Otherwise, this presentation would be too slow.
If you are still worried and you ARE using preshow, just quickly preshow one more person.

CMR would get around this problem. It could even bolster the routine. If your participant mentally changes the last digit to throw you off, you will inevitably divine the trick digit--just as impressive, if not more so, than revealing the actual PIN. You can then circle back and have the participant think of the actual last digit. With CMR you will genuinely be tracking each number as they think of it.

This does present the challenge of blocking the routine. Do you want to reveal the digits to the audience as you divine them? If yes, then the standard CMR method of a board with numbers will work fine at the expense of your participant's privacy (so they better be willing). If not, you can preserve their privacy with a number board that is visible to only you and your participant, at the expense of potentially "third-wheeling" your audience while they wait for you to divine the numbers. Either version poses it's own challenges, but are completely solvable as long as you can anticipate them and stage your show accordingly.