Necron tech isn't effected by Shadow in the Warp

• Sheild of Baal [Exterminatus]:

"Most importantly though, as the tomb world awoke it sent a phase-pulse message out into the void. Its eldritch science was unhindered by the Shadow in the Warp, and the missive flashed through subspace until it was intercepted by the fleet of Anrakyr the Traveller.

...

Turning his fleet towards the glinting crimson orbs of Cryptus, Anrakyr engaged his inertialess drive, his vast Necron armada streaking off into the void. Unlike the ships of the Imperium, those of the Necrons did not travel through the Warp, and so the great psychic barrier cast out by the Hive Mind was no impediment to their fleet."