(Read: The danger of blind spots.) Many new cars have proximity sensors that beep with increasing frequency when you back toward solid objects. The sensor systems might work well as parking aids ...

Radar sensors tie into the system, providing audible proximity alerts and an on-screen ... want something that matches the exterior of your car. Expect this kit to detect obstacles up to 8.2 ...

[mircemk] shows how to create a simple non-contact proximity sensor using little more than an Arduino Nano board, and a convenient software library intended to measure the value of capacitors.