I've been skimming through posts on here for a while researching something unrelated, however since I actually LIVE in Wisconsin and have quite a bit of experience with probation/d.o.c. In wisconsin I figured I'd drop a post.
You do still have rights, however they are rather limited. Yes a probation officer (does not have to be YOUR po) can search you at any time without a warrant. If the house is yours or you are on the lease, a probation officer can search your entire house at any given time without a warrant. If the house is NOT yours and you are NOT on a lease (living with a friend etc.) a PO can ONLY search YOU and YOUR sleeping quarters. They will still try to search the whole house when they do a search, but if you confront them about that they will stop. If a PO does a NON-scheduled home visit, you don't even have to answer the door. However, if they know you are there (can see or hear you) you will get violated for not answering. If a PO does a SCHEDULED home visit, you have to be there and have to let them in.
EXAMPLE: The last time I was on probation I was living with a girlfriend and I was NOT on the lease. To limit the scope of their searches, I claimed the couch in the front room which was right by the door as my "living quarters." This limited their searches to said couch and anything within arms reach of said couch.
All of the above is null and void if you are on the are.O.P.E. (repeat offender prevention ***, sorry can never remember what the E stands for) program. If you are on ROPE, any PO can come to your house at any time (day or night) kick your door in and toss your house whether you are there or not. If you get put on ROPE you will know, they will tell you. You will also need to sign a new rules list. However, recently they've been having people sign ROPE rules right off the bat. They won't put you on ROPE right off the bat unless you are a violent offender or have been on probation multiple times or have had multiple violations, but they won't need to inform you when they do this if it was one of your original rules. If you or anyone you live with is placed on the ROPE program everyone living with that person will need to sign something giving them permission to do this, if anyone refuses then the person on ROPE cannot live there.
EXAMPLE: I've had roomates that were on the ROPE program. Probation officers have done massive damage to my place executing surprise searches. They've done this three times that I was present for. The first time they actually knocked, however it was 3am so there was no way I was answering my door. Within 5 minutes my door was kicked in, I was detained and my house ransacked. My roommate (the only person on probation in the residence) was not even there. D.O.C. Is not liable for any damage done during a search.
DISCLAIMER: I am not a lawyer, this is not legal advice. I am by no means an expert so don't go snappin on me excon... I'm making that clear right now. My advice to you would be to ask your probation officer for a copy of Wisconsin D.O.C. Rules and regulations for probation and parole. If they refuse to give you a copy (i've had this happen) write the department of corrections and request one (you may have to pay for it). That book will tell you everything they can and can't do along with a lot of interesting little bits of information that you may find VERY beneficial.