In order to get a pair of 'eyes' for my device, I would need to look into using some sort of range-finding sensors for calculating distance. I have looked into first experimenting with a cheap option, which is the HC-SR04 ultrasonic sensor which can be bought off sparkfun, ebay etc.

I have hooked that up with my Arduino Uno plus MP3 shield which I already have loaded up with some sound samples I want to trigger in order to simulate a parking sensor in a car. I have successfully done that for one which looks something like this:

I have hooked the Arduino to a speaker but in actual use, the user would be wearing some sort of wireless earbuds or headphones.