Radar can see through fog, smoke and dust, and works just as well in pitch darkness. Which could make it pretty useful for catching creeping adversaries. The HMRS (Helmet Mounted Radar System) might also have some other useful features; the ability to see through foliage, and the ability to see through walls, are described as "desired" capabilities for the HMRS rather than requirements.
The HMRS description also encouragingly specifies that - the effective radiated power of the system has to be low enough not to affect the health of the soldier - and presumably not the other members of the squad either, who are likely to be lit up by each other's radar from all directions. Anyone worried by cellphone radiation emissions need not apply, tinfoil helmet liners optional.
Source: wired.comAdded: 28 October 2009