Requirements for placement of smoke detectors have changed over the years and for the better. The current standard is to have smoke detectors in every bedroom and on every level of the home. And that the detectors must be interconnected so that if the smoke detector in the basement sounds an alarm then all the smoke detectors in the house sound off as well.
Of course I inspect many older homes that are not up to this standard and are not required to be. However I do inform the home buyers of the current standards and encourage them to bring their home up to that standard in order to promote safety.
The good news is that it is very easy to achieve this goal with the help of technology.The introduction of Wifi connected smoke detectors has made it very easy to achieve modern standards even in older homes.
Simply install them as needed throughout the home and they will stay in constant contact with one another. And by the way, this does not require any internet or home Wifi connection. The smoke detectors have their own network built in! It also does not require hardwiring.
There are even more advanced smoke detectors from a company called Nest that will call your smart phone if an alarm sounds in your home!