[NoImmatureAdHom]

Interesting thought! My guess is that it would depend on the size of the blast. I can imagine a scenario where Putin uses one (or a few) dial-a-yield type warheads turned all the way down. The point isn't to blow stuff up, it's to clearly communicate "I am willing to use nuclear weapons".

In that scenario, would a few kt be enough to set off sensors / be distinguishable from noise? I don't know.

Still, a very good idea and worth looking in to.