Accelerometer module ADXL335 Three Axis Low-g
The ADXL335 is a small, thin, low power, 3-axis accelerometer with signal conditioned voltage outputs. The module measures acceleration with a range of ±3 g. It can measure the static acceleration of gravity in tilt-sensing applications, as well as dynamic acceleration resulting from motion, shock, or vibration. The user reads the analog signals at the XOUT, YOUT, and ZOUT pins.
NOTE: This module requires between 1.8 and 3.6VDC. It should be powered using the 3.3V pin on the Arduino not 5V!
Here is a good tutorial to connect this device to an Arduino.