This happened to me about 6 weeks ago. I didn't want to post it right away because I was testing the legal waters and getting a feel for what my options were.
My fiancé was in Chicago for the weekend so I had the house to myself. I fell asleep watching TV in the family room. There was a knock at our front door around 4am. I had woken up maybe 30 minutes earlier and decided to have a snack, so I was still awake when I heard the knock. When I'm home alone and plan on sleeping downstairs, I take my firearm out of the nightstand and bring it down with me, so it was the first thing I grabbed when I heard the knock. At this point I'm standing between the kitchen and the family room with a direct line of sight to the front door. I've removed the gun from the holster and it's down at my side. After the knock there was no noise for 60 seconds or so, and then someone started yelling and claimed to be the police department. My first reaction was that the police were not at the door, and someone was either playing a joke, or worse. Why the hell would the police be at my door in the middle of the night, and why didn't they identify themselves as soon as they knocked? I approached the door slowly and looked out the peephole, but I couldn't see anyone even though the driveway and porch lights were on. I went upstairs and called 911. The operator told me that it was the police, and they were responding to a call about gunshots in the area. This rings a bell because I did remember hearing 3 "pops" way off in the distance, but they sounded like fireworks and they definitely weren't in our neighborhood. There is a 500 acre preserve near our house, so it's possible they came from that area.
So the operator is talking to the officers on the scene, and talking to me at the same time. I ask her if I should go to the door - she debates it with them and then tells me yes. I leave my firearm upstairs and head down toward the door, still on the phone with the operator. She tells me to make sure they can see my hands when I come out. At this point I'm beyond confused. I slowly open the front door and stick both of my hands out before revealing any of my body (the phone was wedged between shoulder and ear). When I stepped out on the porch there were multiple officers with their guns drawn and pointed at me. I was handcuffed at gunpoint and placed on the ground. A dialogue starts and I quickly find out that before they even knocked on my front door, they had jumped our fence in the backyard and were looking in through the rear sliding glass door. Because they saw a light on in our house, this somehow gave them enough reasonable suspicion to become peeping toms. In other words, they could see me when I was standing in the family room with the gun.
I tell them I did hear some pops in the distance but couldn't tell if they were fireworks or gunshots, but they certainly didn't come from our neighborhood. They ask me why I had a gun, as if it's unusual to retrieve a gun when someone knocks on your door at 4am and doesn't say a word. I explain, and at this point several officers look like they were going to enter the house, so I told them that they did not have my permission to enter our home. I said it rather sternly and made it clear by saying it twice. They didn't seem to care and proceeded to do a "sweep" of our home. They didn't search through anything, but they entered every single room, apparently checking to see if anyone had been shot. Two officers stayed outside with me, and one of them said something like "I don't care if you have 10lbs of blow in there, we aren't looking for drugs. We just need to make sure nobody has been shot." After they're done they uncuff me and ask if they can swab my hand for gun powder. I told them I had no problem with that, but they didn't follow through.
There have been a few auto "break-ins" in the area (a couple of high school kids taking small bills from an unlocked car), and while that concerns me - having guns pointed at my head, my house searched, and sitting in my driveway in handcuffs for all of my neighbors to see concerns me far more than minor theft. The following Monday the first thing I did was get the police report, audio recordings of the 911 calls, and audio recordings of the radio traffic between dispatch and the officers on the scene. I talked to a couple lawyers and a family friend that's a judge. The opinions varied a bit, but the judge had the strongest opinion and said that it was unquestionably an illegal search of our home. Whatever the case may be, I felt like the officers' actions meant that the 2nd Amendment and the 4th Amendment were mutually exclusive. Oh well. I reconciled it with the department politely over the phone - mostly because I wanted to make sure they actually believed me. They did, and I've put it behind me although it royally pissed me off at the time.