A system includes a microphone mounted inside a vehicle, a speaker mounted outside a passenger cabin of the vehicle and directed outside the vehicle, a camera with a field of view encompassing a seat in the passenger cabin of the vehicle, and a computer in communication with the microphone, speaker, and camera. The computer is programmed to, in response to data from the camera indicating a gesture by an occupant of the seat, activate the speaker to broadcast based on data transmitted by the microphone; and prevent the speaker from activating in response to data indicating that a biometric characteristic of a pedestrian outside the vehicle either matches a stored biometric characteristic or fails to match any of a plurality of stored biometric characteristics.