As a postscript, I wandered back to the maxbotix website, and found they have quite a lot of helpful looking stuff that you might find useful, including, a page titled

Using an I2C‑MaxSonar with an Arduino:

https://www.maxbotix.com/articles/095.htm

It's nearly 7 years old, so some details might have changed, but should be a good start. They also seem keen to provide technical help, so maybe would answer a query or two if you need it.

Best wishes, Dave

  As I pointed out, I was confused as to whether the datasheet and the DigiKey page were discussing the same object.

However, a second Google provided a link to the (presumed) originator of the datasheet ... so maybe that would be of interest? ... Unfortunately, first glance suggests you might have to rattle the piggy bank for a few more than 10 dollars, but maybe it would pay for itself if it prevented a mishap?

https://www.maxbotix.com/product-category/xl-maxsonar-ez-products

Good luck with your project!

I have no relevant experience or recommendation to offer, but on searching I noticed:

The data sheet (click tiny red PDF button in middle of page) on the web page

https://www.digikey.co.uk/en/products/detail/adafruit-industries-llc/982/5356850?utm_adgroup=Ultrasonic%20Receivers,%20Transmitters

mentions range to over 6m (245 inches) ----

LV-MaxSonar®-EZ™ Series
High Performance Sonar Range Finder
MB1000, MB1010, MB1020, MB1030, MB10402
With 2.5V - 5.5V power the LV-MaxSonar-EZ provides very short to long-range
detection and ranging in a very small package. The LV-MaxSonar-EZ detects objects
from 0-inches to 254-inches (6.45-meters) and provides sonar range information 
from 6-inches out to 254-inches with 1-inch resolution. 
Objects from 0-inches to 6-inches typically rangeas 6-inches1.
The interface output formats included are pulse width output,
 analog voltage output, and RS232 serial
output. Factory calibration and testing is completed with a flat object.
 1See Close Range Operation

The data sheet discusses several different versions ... how this ties up with the single adafruit part offered by digikey is unclear.

I have no idea if it is supported by any of the Arduino libraries.

It might also be over budget. And it might not work...

But it might be worth a look if you don't mind doing some R&D!

Good luck, Dave

Well then, have a happy life.

You sure are a hard guy to please ... :)

OK, build a small wooden frame out of 2" thick wood (so that a car wheel or a shotgun can move over the top of it and have the interior protected). Cut a notch in it to allow wiring to pass underneath it to power the sensor pack.

Inside this frame, place an Arduino and a HC-SR04 sensor pointed UP at the minimum distance from the FRONT wall for the longest vehicle to be placed in the garage and glue the cord into the notch. Run the cord to a convenient power source.

Set the Arduino to flash the overhead lights, sound a siren, fire a cannon ... your choice of attention-getting devices. Set the Arduino to do all of this when the HC-SR04 finds an object within 14" above it (well within the capability) because that means a vehicle has just arrived at the minimum safe distance from the door of the garage.

If you restrict the locations to one specific slot for each vehicle, then place the sensor at a convenient distance from the front door to allow it to close safely in front of that specific vehicle. Doesn't matter whether you drive, back or push it in, the car's the same length in both directions.

Hang a second one (different colour) for reversing in.