Many garrisons have one or more 0 alarms that can be triggered, leading to the arrival of enemy reinforcements. You can manually disable an alarm by interacting with it, which will turn off all alarms in the garrison. You can also destroy an alarm by shooting at it, but this will alert nearby enemies and will not disable other alarms in the area.

An alerted enemy will try to trigger an alarm if he can. If he succeeds, reinforcements will come, which will make liberating the garrison more difficult.

If you manage to liberate a garrison without sounding an alarm, you will receive a CP bonus. If you liberate an garrison without being detected at all you'll get a larger bonus.