The Hermetic Oath is very explicit about not using magic to scry upon members of the Order. What about mundane sneaking up and looking through the window, or hiring grogs to do it for you? Is it only Hermetic magic, or is a magus forbidden from using horoscopes or Second Sight to glean information on other magi?
Can a magus use magic by proxy, such as paying a faerie (who isn't under the Hermetic Oath) in saucers of milk and booze to find out information? What if you have to pay them in spells? Are familiars (with or without their innate magical powers) considered part of the magus for purposes of the Oath?
Are there any canonical Peripheral Code rulings on this? Non-canonical thoughts are welcome as well, ideally noted as being such so it's easier to brainstorm a response.
Spying using entirely mundane means is not covered by the code, but you have to make absolutely sure it's mundane means.
There is space for some trickiness, though.
For example, if you hire a person who has a supernatural ability in the full knowledge they have a supernatural ability (though you had no hand in their developing said ability), and that person utilises said supernatural ability to aid them in their spying while you personally don't cast a single spell... is that magical scrying?
What if you hire a faerie to do the spying, using no magic to compel said fae?
Or you get some fun stuff: if you use a magical spell to enable you to communicate with a spirit, but use no compulsion magic upon the spirit in convincing it to spy for you, are you guilty of using magic to spy?
My understanding is that if a Magus gains knowledge of another OoH member via any use of magic including but no limited to items that can make the user invisible or change their shape or disguise them. This would include ( IMHO) speaking to a spirit or stone or anything via magic so it can tell you what it saw. The key is using magic. so the above example with asking a Fae to spy for you is perfectly fine.