What happens when the SD card is full?

It will automatically begin to overwrite over the existing recordings, frame by frame. So if an incident occurs, it's important to save it locally to your device/smartphone to prevent the video from getting overwritten. Also keep in mind that this product can support up to 128GB micro SD card in case the 32GB micro SD card that's included is not giving you enough recording time.

A 32GB card with continuous recording will last up to 4 days before the footage starts to overwrite the card from the beggining. 

A 32GB card with event recording (recording motion detction alone) can last up to a a month or more before the footage starts to overwrite the card from the beggining. This all depends on how much motion there is in front of the camera.