I know that you are supposed to change smoke detector batteries when the time change, but if you have not change them today.  Please do not become a statistic.  If your home is older than around 10 years, you probably only have battery operated detectors. They now sell detectors that use 10-year lithium battery’s that are much more user friendly than in the past. If your home is newer than around 10 years, then you probably have both hardwired and battery back-up detectors.  These batteries will need to be changed twice per year and tested every 30 days.  Please at Know Before You Buy Home Inspection we do not want to read or hear the news of tragedy.  CHANGE THE BATTERY