Amazon has added the ability for 4th-gen Echo and 4th-gen Echo Dots to detect occupancy in a room by emitting an inaudible ultrasound audio wave. The capability can be used to automatically trigger Alexa Routines when you enter or exit a room. When configuring the trigger of a routine, select “Smart Home” and then select the appropriate Echo to be given the option to trigger the routine when “People are detected” or when “People aren’t detected.” You also have the option of enabling or disabling ultrasound motion detection altogether for each compatible Echo device. This is done under the device settings of each Echo within the Alexa app.