How to Replace First Alert Smoke Detector Battery 

Perfect, thank you! ETA: if still beeps after changing battery, make sure the base is properly seated. I replaced battery, still beeping; pressed reset button, still beeping; called for new unit, and after removing unit to provide model#, I reattached the unit in a way that must've made a difference. It hasn't beeped for 4 hours - I think we're good 😊

Thank you, this helped! One difference for my unit was that it did matter which way the positive and negative was positioned.

0.24 The does matter the polarity is printed inside on the top

Thank you for simple instructions

My First Alert (SC9120B) looks identical from the front (label on back is a bit different). It comes with a plastic locking pin installed from the back; there is a little black dot on label where this is printed. To open battery tray you peel back label edge where dot is and pry pin out with knife. Battery tray contacts-end is single orientation slotted on mine

I installed a new battery and hit reset I noticed there is a green light The light is steady and not flashing Which is correct

With mine I couldn't open after pushing thing won't snap open

couldn't get the battery out

This was super helpful! Thank you so much! 🫡🙌🏾