Brightly coloured pixels denote objects that are closer to the depth sensor. Black pixels denote sensor noise caused by reflective, metallic objects. The radio sensor shows a micro-Doppler signature of a moving object, for which the x axis denotes time (5 s) and the y axis denotes the Doppler frequency. The radio sensor image is reproduced from ref. 89. The acoustic sensor displays an audio waveform of a person speaking, for which the x axis denotes time (5 s) and the y axis denotes the signal amplitude.