I would base your automatic alarm response on the staffing level of your companies.
If your staffing is three or four members to a unit, I would send one engine, one truck, and a chief to an automatic alarm. If your unit staffing is less, I would send two engines, one truck and a chief. Naturally, if the automatic alarm was followed up by a phone call reporting a fire, I would upgrade the response to a full assignment ie four engines, two trucks, a rescue co., and a chief.
Also, you can have a tiered response based on alarm activity.
For an automatic alarm the normal response is two engines, a truck, and a chief, Call this a Level 1 response. If you have increased alarm activity, have a Level 2 response of any two available units.
If you are experiencing numerous automatic alarm responses during a weather related event or electrical power outages, have a Level 3 response of any one unit.