Welcome Llew to HD talking, there is a lot of info on the alarms system, and plenty of fellow riders here to help. Do a search in the tabs above or go to self help section. Smart Siren I does not have the chirp and cannot be retro-fitted with Pager option and was designed around the button activated fobs. Smart Siren II has the chirp and is compatible with the wireless Pager option...your choice depending on if you are looking for the future Pager option or not as the price of the units are the same. $100...HD imagine that! :laugh