[dantle]

Perhaps the "all at once" attack could work against today's hardware. This is because the mics (in devices I know of) are co-planar and the user may be speaking to Alexa (or whoever) from directly above or below the device. In this configuration, it is valid for all mics to be receiving the same audio signal simultaneously.

But in some future rev, one could imagine that if the mics in the array are non-coplanar (e.g. at least 4 mics) and sufficiently far from each other, then there is no possible way for the audio signal to reach them at once (unless it is actually light being measured).

[MauranKilom]

You could add timing difference to individual lasers as necessary. It's not really more complicated than duplicating the laser setups and feeding them the same signal with time delays. Not a huge step.

However, non-coplanar mics would work for the opposite reason: If they are on different sides of the device, you couldn't reach all of them from the same distant location. So unless all mics receive (more or less) similar sound signals, you could discard it as manipulation.