checho0180 wanted to give his dad and extra help when parking in his parking area. Instead of designing a classic built-on-bumper parking sensor with ultrasonic transceiver pairs, he went the other way. He designed a transmitter module with an ultrasonic pair which is fixed on the garage. This module then wirelesly transmits the distance to a receiver module inside the car which has an LCD to show the number.
This is the transmitter with the ultrasonic pair on the garage side:
All details in his instructable page
And you may now ask yourselves, why not making a parking sensor on the bumper of the car??? Its just a matter of taste, and (i think) dad would not allow his son to put holes in the car...