Hello,

If the "child" install has its own Product GUID, then yes. You can use the same method to detect it. If it does not have its own Product GUID then Windows does not know nothing about it. Then the only way to "detect" it is to see if "child" specific files are already there with a specific version resource (because you said you do not write anything to the Registry). You can use "If File/Folder Exists..." and/or "Get File Info (Version Resource)...".

BTW, if you have access to the "child" install sources and it does not have its own Product GUID, just let the "child" install write a simple registry footstep to the "main" installs Product GUID registry key (e.g. AddOnVersion=1.2.3.4) and you can detect it without an unique GUID.

Friedrich