[wix-users] How does Burn detect if it's installed

[Vanniekerk, Tyrel (GE Healthcare)]

I have a custom BA based in the WixBA and it handles the DetectBegin event.  In that event, the e.Installed value shows up as false, even though the bundle is installed (Shows in Programs and Features).  When I look at DetectPackageComplete, it shows my MSI as Present.  I did recompile the bootstrapper.  So how does it detect if it's installed?  Is there a hidden product ID or does it use the UpgradeCode?  I looked at the WiX source code, but could not find where the Installed value is being set for the DetectBeginEventArgs argument.

Thanks.