There doesn't appear to be a way of detecting if an URL is truely remote, i.e. something that doesn't point to a resource on the local system.  Slim::Music::Info::isRemoteURL does no such thing - it returns true for anything that matches
/^([a-zA-Z0-9\-]+):/ and is a registered protocol.  This includes URLs such as db:album.titlesearch=1 and also things like randomplay://artist.

The alarm clock code needs something like this in order to know if it makes sense to pause the currently playing track on snooze.  For example, radio streams shouldn't be paused as the user would then wake up listening to non-realtime radio.  Actually, I guess what the alarm really wants to know is whether a given URL points to "live" music.  isRemote is a good enough approximation, however.