You need to have access to special Subaru Monitor software which connects to the ODB2 port. I figured it was cheaper to just visit the dealer to get it enabled and adjusted
I recently installed the shock sensor module myself (super simple to do), but the only way to enable the module and set its sensitivity is through the special software connected directly via the obd2 port.
When my dealer enabled the module - they charged me $50 and set the settings to medium (medium setting seems good) but from what I read the sensitivity is a setting from 1-10 (10 being the most sensitive).
Edit: Directly from the installation instructions for the 2016 crosstrek perimeter alarm:
Impact Sensor set up procedure: (Subaru Select Monitor required)
a. Select 'Subaru Vehicle'
b. Select 'System Check'
c. Select 'Integrated Unit'
d. Select 'Customizing'
e. Select 'Impact Sensor' and change to 'ON'
f. Select 'Impact Sensor Setup' and change to 'ON'
The Impact Sensor has two levels, warning and alarm. In warning mode (light impact) and the alarm will not trigger but instead will give two horn chirps and two light flashes. Heavy impacts trigger the alarm along with tilt/tow detection.
In the event that the vehicles impact sensor is too sensitive or not sensitive enough it can be adjusted. Please contact an authorized Subaru dealer for assistance.
So looks like we don't have access using basis tools and probably easier to go to the dealer to have it adjusted.. (they might charge you $50)