I found that a 32GB SD card, works fine, and gives a good few days recording. I do find I have to clean it up every few months, as the "Event" videos don't get recorded over, and it gets to a point when it is full. I keep meaning to try a larger SD, but formatted in FAT32.I have had a UTR problem of my own making. The UTR comes with an 8GByte Micro-SD card. These cards go up to 512GByte. I thought I would try a 128GByte Micro SD card and all was okay until the card filled up. What should have happened is that the UTR then starts writing over the earliest entries. What actually happened was that the UTR hung. I went back to the 8GByte Micro-SD card and all was okay. I then tried a 32GByte Micro-SD card and again it was okay. So, the actual maximum Micro SD card that the UTR firmware will process correctly is 32GBytes.