Jason writes -
Ed Paradis has put some thought into a couple of hacks for the Hot Wheels toy radar gun. You can use the radar to detect the speed of moving objects, but Ed also posted some semi-successful (and some not-so, but worth reading) experiments with using the device in a custom circuit to detect the distance of objects for robotic projects. It’s also worth noting that the LCD can be repurposed as a display output for your other electronic gizmos. For 30 bucks, it’s a pretty good collection of useful robot parts.