Actually, the rules on preparations are pretty clear. There are 3 types of triggers:
Command, which means the spell is triggered by you. You have to be on the same plane AND have line of sight to the object.
Contact, which means the next living being to touch the object triggers the spell.
Timed, which means you set a specific amount of time and then the spell goes off, like a time bomb of sorts.
What you are asking for in your post is for the ability to set the trigger on an object, then carry that object around, and then set it off as you need to. That's Command, it's covered pretty explicitly in the rules. So, I have to decline your request on the Contact trigger as there is another trigger that already covers what you are asking for.
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I've put together the map we'll use for this encounter, and I've done so using Ditzie. To be clear: You do NOT have to download anything! This is all online, and it's completely free, and you don't even need an account to use it. I have one because I've got several folders of art out there that we can use for mapping, but even that was free and costs me nothing.
To state it again: You need to download NOTHING, you need NO account, and you need to pay ZERO. Are we good with that? Cool.
To use Ditzie: I'm responsible for putting the map together and adding/removing tokens. You are responsible for moving your token around on the map to wherever you need it to be. For the purposes of our initial encounter, each square in the grid is 2.5 x 2.5. You each take up 5x5, or a total of 4 squares (2 left-to-right, 2 up-to-down).
To move, all you need to do is left-click and hold, then drag your token to where you want to be. Once you've done that, hit the enter key. The URL in the window will change; copy and paste that into the Map thread (which I will be creating here shortly), and voila! The map is updated. Remember to use only the very last map link. Not doing so may cause errors, overwritten movement, and/or getting messages that you need an account, and that is not correct. It's just Ditzie's way of telling you that you have clicked the wrong link.
I've placed you all on the map outside the restaurant to start. This is not important other than to show you that you are on the map. You are free to move yourselves wherever you need to be; once anyone goes inside I'll update the map with patrons and such (I mean, you can't see them from outside, can you?).
If there are questions, just let me know.
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Information from contacts: Quiet night. Too quiet. It's almost like asking about the Fratelli's is taboo what with all the silence you're getting. Or maybe it's just late and people are sleeping?