Drive Smarter runs in the background if you've given it permission to do so. It does that so that it can continue to provide telemetry to your radar detector for Drive Smarter services such as Posted Speed Limits, and Community Radar alerts.

If you'd prefer it not do that, then when the app is not in use you can close it. If you don't know how to do that, you can find links to instructions for both Android and iPhone below. You can also disable mobile data access in your phone's app permissions, but this will impact operation when it is open in the background.

Android

How to Fully Close Apps on Android

iPhone

How to Fully Close Apps on iPhone