Okay, so in this case, there is a piece of information you wish for them to glean from the environment. How you make use of this in ARIS still depends on how you want their experience to unfold.
Let's say you wanted them to not be able to proceed in the game unless they got this date. Then you would create a plaque that says "Hooray, you got the date correct". Then you'd make a trigger for this plaque, a QR type trigger, and enter the date into the alphanumeric field.
For the next part of the tour/game, the next location, you would have a lock on its trigger:
player has already seen "hooray" plaque
That way the player could not go to the next location (or see it on the map) until the opened the decoder and entered the correct date.
But this is just one possible scenario (and one way to enable this sort of scenario). For instance, if you use a conversation, you can send the player directly to the decoder and even give the decoder a temporary message that asks them to enter something specific.
There's no reason why they couldn't integrate ARIS with other stuff too. If they need to take notes, this could be done in other apps or with pencils. Great way to have teamwork no doubt.
Once you think of a few ways to play around with how you can use environmental information, I'd suggest too to consider how the finding of information contributes directly to the experience you're after for them. Is this like a scavenger hunt or the National Treasure movies, where the information hides secrets they want to know? Is the information something that allows them to understand something more deeply? As in History class, it is easy to ask for dates when what you really hope to get from students is a deeper sort of engagement.
I'd love to hear more about what your ultimate aims are once you start figuring out some of the technical stuff here.