The court has received briefs on a case involving former Waunakee High School chemistry teacher Mark Jahnke.
The 44-year-old Jahnke said that because his girlfriend agreed to be naked in his presence, she had no reasonable expectation of privacy.
The state Department of Justice counters that shared intimacy does not give one the right to film the other.
The case tests Wisconsin's video voyeur law, most recently enacted in 2001 as inexpensive recording devices spawned Internet fetish and voyeur sites.
There is no timetable for a court's decision on the case.