I posted this a few years back but it's worth posting again for all the newer members . . . .
IF your Street Glide, Road Glide, Road King or Ultra has a factory security system, here is a economical way to add an alarm / siren.

You can purchase these Piezo alarms cheaply on Amazon (I bought one for about $12) and wire them in yourself to factory supplied connector or, you can purchase with connector & double stick tape already installed on eBay (search eBay Harley alarm siren). for less than $30. They work perfectly with chirps as well as a loud siren just like the $100 OEM from Harley.