On your paired iPhone, tap Settings > Apple Intelligence & Siri (or Siri ) > Talk to Siri, then make sure that Listen for “Hey Siri” or “Siri” is turned on.

On your Apple Watch, tap Settings > Siri, then make sure Listen for “Siri” or “Hey Siri” is turned on.

Turn any other Siri options on or off.

For more information, see Use Siri on Apple Watch.