[ALittleLight]

It's not valid for the state to collect evidence illegally. If it was then it would make sense to have any laws constraining how the state could gather evidence.

In this case it's not the state that's spying, it's the landlord, and the landlord is constrained by the punishments for violating the law against spying.

A slightly different spin on it, if the landlord witnessed a murder while illegally spying on his piano should his recording or testimony be admissible in court? I would say yes though again the landlord should face whatever spying penalties apply.