You can use a Ring Video Doorbell without a subscription, but you’ll have a very limited experience. You’ll receive basic notifications when motion is detected, or the Ring doorbell button is pressed, and you’ll be able to view the live feed from the camera and talk to whoever is there.
You won’t get any recorded Ring videos so, if you miss the event, you won’t be able to check up on what happened. You’ll also lose virtually all the smart notification features that the Ring doorbells provide which allow you to tailor what you get push notifications about and get only the alerts you care about.