I fitted an alarm a couple of weeks ago and mine was in the passenger door but it was loose, partly held on with masking tape and the mechanism was very stiff so im not sure if thats the standard place.
Should be located on Drivers door. Its about half way up and has a white cover on it on most honda's. Its just the control relay for the locks. You have to unplug it if you use an after market alarm. You can then tie into the door lock wires in the drivers footwell. You will need to relays for this to work as well. Sorry dont have any pics to help out.