Smoke alarm batteries should be replaced annually, you should choose a date or event that will prompt you to remember this and change the battery on this day each year. Many people recommend the start of Day Light Saving as an event that will prompt this. Most smoke alarms take a 9 volt battery – these are the small rectangular batteries with the male and female lugs on the top of them. The smoke alarm will sense if the backup battery is low and will emit a Chirping sound approximately every 30 seconds, should this happen simply change the battery and this should silence the chirping.