The shield button on the home screen is used to enable or disable monitoring mode. When monitoring mode is disabled (button is switched to gray color) then the camera will not detect or record any events, even if the camera is open. So, when you want the camera to stop recording events, you can either close the camera or turn OFF monitoring mode.

For example, when you want the camera to stop monitoring and recording what’s going on, e.g. a private moment, but your camera device is unreachable. You can still turn it off from your viewing device.
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You can also enable or disable monitoring mode based on location or time schedule by using Apple's Shortcuts app. AiCam has integration with Siri shortcuts to automate your workflow. See this tutorial for more details.