This made me chuckle, from Advanced Usage:
Oh I'm sure you'll figure it out
Also, it seems like this could have home/business security applications as well...
You don't use ultrasound because it has both resolution and absorption issues.
I've used both these laser sensors and those dirt cheap ultrasonic sensors in many projects. The ultrasonic ones would work just as well in this application, and be 10x cheaper. The biggest difference is the size, as the ultrasonic ones are pretty bulky in comparison.