You can indeed order additional sensors once your initial one is depleted. You can place an order for new sensors at any time through the app by navigating to the upper-left side menu, then going to "Buy more sensors." Each sensor costs $129, and they will be shipped to you for free. It's up to you how often you'd like to receive a new sensor.

While your membership provides a new sensor every 3 months, you're welcome to order them more frequently if you choose to do so. One sensor typically lasts for approximately 14 days.