I have two switches that control one light. When installing Decora Smart® Z-Wave switch, do I need to replace both switches?

Yes. If you have two switches that control one light and want to control the light with a Decora Smart Z-Wave switch or dimmer, you will need to replace one switch with a Decora Smart Z-Wave switch or dimmer. The other switch would be replaced with a Decora Smart Companion:

• DD00R-DLZ - Decora Matching Dimmer Companion – use for 3 or 4 way dimming applications
  
  
• DD0SR-DLZ - Decora Matching Switch Companion (with Status LED) – use for 3 or 4 way switch applications
  
  
• DD0SR-1Z - Decora Coordinating Switch Companion (no Status LED) – use for 3 or 4 way for switch applications

Watch this video on Installing a Decora Smart switch with a matching companion