You cant "lose" your right to refuse a search, and you cant "lose" your right to refuse entry by the police.
You can agree to either if asked, thats not the same thing.
As far as entry into a home, there are a lot of people who think they always need a warrant. They dont. There are many circumstances under Federal law in both Canada and the USA that allows police to enter under certain circumstances, examples include witnessing a felony being commited, or being freshly pursued by police, those are just two. I wont bother with a 10,000 page list of them all, but there are a few out there, and of course, every state in the USA has a seperate state criminal code as well, so it depends on where you live.
Most police are well versed in what circumstances they can demand entry, or a search of your person, they do it for a living. Many people get themselves in hot water by assuming they know the law, when they dont. That being said "always know your rights" I agree with 100 percent. Be informed.