[dwheeler]

At 40 mm, it seems basically useless as an attack in almost all circumstances.

However, I wouldn't write it off completely, because if somebody else can extend its distance further then I can see it becoming a concerning attack.

[kurthr]

I'd agree, requiring in-room access makes it not that big a deal. There are other attacks (like measuring the radiated emissions) to detect finger coupling remotely that I'd be more concerned about. Those could detect private user input and could be hidden nearby.