A:AnswerN842 is newer. The biggest difference is that N842 contains newer smart motion detection features. The Safeguard is part of the motion detection features. It is able to detect objects missing or left behind. NOTE: The recorders have 8 channels. You can connect up to 2 wifi cameras, each one of them would use a channel. So, you can have 6 hard-wired cameras and 2 wireless cameras.
A:AnswerIt depends on the hard drive capacity, number of cameras, camera resolution, storage schedule, bit-rate, fps, etc. Please check our Lorex storage calculator: https://www.lorextechnology.com/articles/NVR-DVR-Hard-Drive-Storage-Calculator