I would recommend just clicking the Sentry checkbox in BI for a few of the cameras where you would prefer getting human detection. This starts your 15-day trial. The front of the house is a common camera just because you want to avoid false alerts and be alerted when a person is by your house.
More details on activating the camera and pricing here: https://www.smarthomesentry.com/blue-iris
-- Sam from Sentry
