I remember a smokey basement fire we responded to in the middle of the night many years ago where fortunately, all the people in the house had escaped the fire and were standing on the front lawn when we arrived.
Funny thing though, they only had one smoke detector in the entire house and it was in the kitchen, so of course every time they burned the toast the detector sounded. They got tired of it happening all the time so rather than move it to a better location, they simply removed it entirely and stuck it in a drawer.....outta sight, outta mind.
Luckily the smoke was heavy enough that it was able to get into the drawer and activate the alarm and save their lives.
So, even though their not always in the ideal location, they can still save your lives.