Accelerometer can be found as expressions in the Touch plugin
You want to compare the values of AccelerationX, AccelerationY, AccelerationZ or AccelerationXWithG, AccelerationYWithG, AccelerationZWithG or still Alpha, Beta, Gamma to see in what axis the device is being rotated/turned/etc...
You likely should use the "Compare two values" system condition to do so.
Not all devices actually do allow browsers/HTML5 technology to take advantage of the accelerometer, so be sure to check on your device.