The Ultrasonic Sensor is a high sensitivity, directional ultrasonic sensor. With the ability to detect a 3cm object at a distance of 2.4m it is perfect for most applications.
The SRF005 ultrasonic range sensor detects objects in it's path and can be used to calculate the range to the object. It is sensitive enough to detect a 3cm diameter broom handle at a distance of over 3m.