We had 2 in a 3 room 1 floor appt. It doesn't matter how many you have they don't always wake you up, the wife shook me and said the house is on fire and I told her to go back to sleep, she was dreaming. We were literally suffocating in the smoke and I still didn't realize the alarm was going off .All you can do is make sure your alarms are operational and that you at least have enough to cover the entire living space .I have spoken to several long time FF one retired cheif with 40+YOS and they all agree no amount of training can prepare you to waking up in hell. We were under the blankets and we got covered in head to toe soot and when we opened the window to get air the place flashed over, only room that wasn't engulfed with flames was our bedroom the wife dove out the window and I thought she paniced and went for the door so I spent several minutes looking for her before I saw she was outside. I then went back in looking for my dog before I dove out the window only to see the roof was on fire above the bedroom. I went up the back stairs and went back in to try and save my dog again but the smoke and heat was incredible by this time, I slid head first on my back down a 2 story wooden stairway to get away from it .I wouldn't wish my worst enemy to have to go through a house fire it truly is the worst experience I have every been in and I applaude the guys in the rubber boots that run towards the fire while everyone else is running away it is crazy inside a house fire and they go in on there own free will to save us .another fire saftey tip is make sure you have a fire extinguisher in the kitchen you never know what can happen.