Cool idea and application! Maybe once @geiser figures out how to connect an upsized horn to the 12V battery, the same connection approach can be used for your front-end camera.
It's too bad that the parking sensors don't have a wider (hi/lo) reading range, rather than being for 'straight ahead' objects. I've been backing into MANY more parking spots lately (or intentionally looking for spots without parking blocks) to avoid the risk of front fender grinding...