If this is targeted at low power microcontrollers, I don't understand how the devices are supposed to recognise the attention word ("Alexa" by default in Echo d

If this is targeted at low power microcontrollers, I don't understand how the devices are supposed to recognise the attention word ("Alexa" by default in Echo devices) and filter out unwanted chatter. Our maybe doing that filtering is cheaper than I expect it to be ? If Alexa ends up in many devices in the same room, which one am I addressing when I use the attention word ? Are we going to have many different attention words for different devices ?