Wouldn't it be possible to, in app, have an option for eah lock to toggle notifications? That way, someone who closely want to watch and get notification on a specific lock (which, I'd assume, the number of autorized user could be set to only one or a low number) ?
That way, a lock with a high number of lockee could have disabled notification off, but someone with small number of lockees (I can think of couple's dynamic here) could activate it without troubles...