The 2GIG-SMKT3-345 smoke detector requires 3 AAA batteries, which can be purchased at your local hardware, mass retailer, or battery store.
You may also order these online here or at your preferred online retailer.
1. Twist sensor counter-clockwise to remove from base.
2. Remove and replace 3 AAA Alkaline batteries.
3. To clear low battery alerts from your panel, see the following article: How to Clear Alerts on the GC2.