Please follow the below steps to complete your battery replacement for the following Ecolink key fob models (images can be found at the bottom of this article): WST-100 DSC, WST-101 GE, WST-102 Honeywell and WST-102 2GIG GoControl.
1. Push on the black tab, then pull the key fob up to remove it from the metal holder
2. Insert a coin into the slot on the bottom left of the unit and twist it to open
3. Slide the CR2032 battery out of its holder to remove & replace it
Ecolink key fob models, shown for reference: