A SpectroWATCH is a change to the model type. So, any model created in the database using the same model type will automatically inherit the watch and any model that uses that model type as a base model type will also inherit the watch.
If you want only specific models to actually use the watch, then create the watch inactive by default by not checking the "Active By Default" check box in the Properties tab when creating or editing the watch.
Then, activate the watch only on those models you wish to use the watch by doing the following:
1. Select the model
2. Click on the Information tab in the Component Detail panel
3. Find and expand the Thresholds And Watches -> Watches subview
4. Find and select the watch in the list
5. Click on the "Activate the selected watches" icon. The set of glasses with the arrow pointing to the right.