Most cars have ultrasonic sensors for parking and radar for longer range detection, such as cruise control.

Every single car from every manufacturer that has PDC sensors in the bumper, which are typically visible as 4 circular sensors on the surface of the bumper.

Wikipedia says both ultrasonic and electromagnetic are used: https://en.wikipedia.org/wiki/Parking_sensor

One of the references is for a Mercedes system that uses ultrasound

I hear some car alarm sensors when passing by, the ones that will trigger when someone is about to park too close and hit the armed car.