The new Echo Flex has this feature though. The mute button electronically disconnects the microphone. This feature is highlighted dominantly in promo materials.

The new Echo Flex has this feature though. The mute button electronically disconnects the microphone. This feature is highlighted dominantly in promo materials. No transparency/visual verification though. The problem I see with this - other than being cool - that it requires motion, so more likely to fail with time.