All light is radiation because it is simply energy moving through space. Millimeter wave is just a kind of electromagnetic wave, similar to mobile phone

communication signal, but with higher frequency and closer range, and it's non-ionizing and not enough energy to damage cells directly, so mmWave

is very safety. 

Sensors are miniature, cost-effective and function without any contact with the human body. They are completely safe since mm-Wave frequencies do
not penetrate the human body, they have characteristics of light, and their output power is 100 and more times lower than mobile phones.