IR sensor + arduino = Car back up sensor?

I am looking to build a car back up sensor. Basically make a beep with piezo buzzer if less than 4 inches left or display on the lcd the distance left between you and the other car. Have the sensor mounted near licence plate. My question is, I was thinking of using this, http://www.adafruit.com/index.php?main_page=product_info&cPath=35&products_id=164 is this a good tool for a job or should i stick with something like this: http://www.adafruit.com/index.php?main_page=product_info&cPath=35&products_id=172

If it will be mounted near my licence plate, what are the cone angles of the area it covers? Meanign how do i align it so that it senses objects. Is this one line/beam that it shoots out or like a sonar (depthfinder) cone angle?

Thanks for any feedback

R

Feedback is welcome.

I would go for the ultrasonic one, they are much more reliable. However they are nether very suitable for what you want. It says on the website about the ultrasonic one:-

Objects from 0 inches to 6-inches range as 6-inches.

Is this one line/beam that it shoots out or like a sonar (depthfinder) cone angle?

They are all cone angle ones, the only straight line one would involve a laser.

Also installing stuff in a car is tricky because of the interference on the power supply.

You might be able to power it off the reverse tail lights. That way it would only come on when you are in reverse. Check the voltages for the wires with a multimeter.

Those ultrasonic sensors aren't environmentally sealed and they don't like water.