Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for motion detection using a communication channel carrier signal. In one aspect, a method includes, for each of one or more communication channels, wherein each communication channel has a center frequency that is different from the center frequency of each other communication channel: determining mean power levels from consecutive power samples at the center frequency, determining a difference between the mean power levels of two consecutive power samples at the center frequency, and determining whether physical motion is occurring in a monitored area based on the difference between the mean power levels.