Accelerometer - BleepLabs/Arduino-Light-And-Sound GitHub Wiki
The accelerometer breakout board we're using is similar to this board but I made it a long time ago before it was available from Adafruit but never put it in a product.
Usage instructions in this code.
It connects easily to the Teensy with just 4 pins:
'G' - Ground, anywhere on the the blue row
'D' - i2c data, Teensy pin 18 aka A4
'C' - i2c clock, Teensy pin 19 aka A5
'+' - 3.3V power, anywhere on the the red row