Used to work for a place with a touchless car wash. Had multiple idiots try this.

The car wash had 8 sensors in the interior that measured the distance between the physical object inside and the structure. This was both a safety feature to make sure it is actual cars and to start the car wash function.

It will (in my case anyways) throw a foreign object alert (or sometimes not even recognise anything in there) to whoever is in charge and they will use their emergency stop switch. It's also covered in cameras in the interior and exterior.

This was all on top of needed valid payments before entering the car wash structure.

Of course this depends on the establishment - older ones probably don't have the safety features.