Also the scatterable surveillance cameras used in his other great novel, 'The Peace War' [0]. Although IIRC they were the size of seeds or similar.

[0] https://en.wikipedia.org/wiki/The_Peace_War

3 or 4 mm in diameter, according to a scene in chapter 6, big enough to have similar resolution to that of a human eye, according to Paul, but able to look in any direction without physically rotating.

In chapter 13 the enemy describes them as using Fourier optics, though that seemed to be their speculation - not sure whether it was right.