SRF10 - The Worlds Smallest Dual Transducer Ultrasonic Ranger

Max Analogue Gain - Variable 40 to 700 in 16 steps.
Connection - Standard I2C Bus.
Timing - Fully timed echo, freeing host controller of task.
Units - Range reported in uS, cm or inches.
Small Size - 32mm x 15mm x 10mm height.
Voltage - 5v only required
Current - 15mA Typ. 3mA Standby.
Frequency - 40KHz
Range - 6cm - 6m.

Full Technical Data, and the sonar FAQ