It is also good to remember that every drone and vehicle has a built-in commlink. The Firewall/Response/Signal/System ratings for these commlinks are, by default all the same.
Standard, commercially available: 3
Security-level or police-level (usually with a Availability of #R, but check flavor text): 4
Military-level (usually with Availability of #F, but check flavor text): 5
These commlinks can and should be upgraded just like a commlink, because the max rating for any programs run on the drones (into autosofts) are still limited by the System Rating, drones can be attacked in the Matrix (hence Firewall), use Response for Reaction when operating autonomously (and Agility for anything unusual, like an anthroform juggling) and need to be in mutual Signal range with your own commlink (hence Signal for long distance usage).
Firewall and System can be bought, as detailed out of the main book (Rating 4-6: Rating x 500 for Firewall and System separately). Response can be upgraded as detailed in upgrading commlinks in the main book (max: Original Rating +2 or 6, whichever is less). Signal can also be upgraded like a commlink (max: Original Rating +2 or 6, whichever is less), but drones / vehicles can also upgrade their Signal through their Sensor Package.
Equally as important is the make-up of the Sensor Package. Drones and Vehicles do not, by default, have the same five senses that metahumans do (sight, smell, hearing, touch, taste) and thus need to have components of their Sensor Package make up this. However, drones and vehicles have more 'senses' to choose from (radiation detection, laser microphone, MAD detectors, etc) and thus when building your Sensor Package, cover your bases equally. It is entirely possible to have a Sensor of 6 on a drone that can't hear anything because you forgot to add some sort of microphone. Arsenal has the default sensor package for a vehicle, but drones require some 'interpretation' of the flavor text.