I am not 100% sure if all Focus have the alarm pre-installed. You just need to check if you have a plug on the hood lock (probably the hood lock do not have the switch inside so it has no pins) and the siren wire. The siren wire you can found it in the right side of the car behind the plastic trim cover that goes on the right side of the rear seats back. Is on the same place of the parking sensors buzzer. The siren only needs one positive wire as the ground is provided by the support to the body.
nuno, thanks for your answer.
So, in SW it would be on that compartment on the right behind the foam? There is where the parking sensor buzzer would be on the SW... btw, in there is also where i installed my sensor box... i remember seeing there some kind of wires... maybe it's better i take a photo...












