The Vira UVC T8 Tube features a built-in microwave sensor that detects occupancy, for safety. When the UVC light is turned on, a warning sound can be heard for 18 seconds, alerting occupants to vacate the room. After 10 seconds, the UVC light will illuminate. If, however, presence is detected, the light will not turn on. If unexpected entry occurs once the UVC light is turned on, the light will detect and turn off.