Can I get your thoughts on this before I approach the person?

I’m back substitute teaching. Today I was at a middle school and they had a fire drill. It just so happened that today I was more of an assistant than a teacher because there was another teacher in there so I just helped out.
I noticed that after each class had gotten outside, the kid at the front of the line was holding up a green card. On it was written “All the students in my class are accounted for except the ones who were absent.”
I’d never seen that before, and I think it’s a great idea.
Only problem is, if I had been in the class alone, as a sub, how the hell am I going to know if all my students are accounted for? Short of taking roll, which half the time I’m not even provided with a roster sheet, AND I don’t know any of their names….well, it’s a problem. Even if I had a roster, if it’s an emergency, we need to know sooner than the time it takes for me to read off 30 names.

When I had my daycare I implemented a “buddy check” thing. Each pair of kids were assigned to each other as a “buddy.” When we went some place, every so often I’d sing out “Buddy check!” and the kids would call back affirming their buddy was with them. They weren’t required to do any other thing for their buddy, except check their whereabouts when the call went up.
My idea is if each teacher could pair up students in his or her class for this purpose, you’d find out in an instant if there is a kid not accounted for.
Somebody could say, “Buddy check,” over the intercom and instantly every kid in the school would be accounted for.

What do you think of this idea?