The current mainstream setup is a wireless Wifi IP CAM at right, and a PC anywhere in the world where you want to monitor or record the video. The cheapest CAM is about $100. The security version with a metal housing can cost 10 times more.
You also need a Wifi router (<$40) to receive the video, a broadband modem and of course Internet connection. Off-site monitoring and recording is as secure as your telephone line (DSL) or cable TV line, which are pretty easy to find and cut depending on areas. Another disadvantage of this kind of system is that you need a PC, which is the obvious target to smash when intruders get through.
The other concepts are small portable self contained devices that can easily be hidden. They are easier to use than a camcorder and there's no need for installation. You can even bring it to a hotel!
The system on the left includes up to 4 wireless quarter sized cameras that can easily be hidden somewhere, and a palm sized monitor and recorder, which can also be hidden somewhere. For the less than $200 system, you can have multiple systems hidden in different places for redundancy.
Using SD cards, you can record several hours of DVD sized video. The system used to come with an 20GB internal hard drive, which will last about a day of continuous recordings. Using half sized resolution, which is still better looking than analog VCR systems, the record time will last for days.
The new systems come with a USB connection, which probably allows you to record video on an dirt cheap external hard drive. The old 40GB and 80GB that people throw away are about the same size. You only need to buy a few dollar adapter and you can record continuous for many days.
Even if you can record for days, you may want a security aware DVR system that don't need any attention, 24/7/52. The DVR at right works with any NTSC or PAL signal. Recording only starts if motions are detected on the images. The detection algorithms are primitive but the storage space is drastically reduced - even if you have a lot of moving tree branches, pets and wild animals etc.
The new videos or images override the old ones automatically. So if you have a large enough SD card, you know you always have a week of most current video stored in the device. A 4GB SD card can last you for months. The video quality is comparable or slightly better than VCR systems. The frame rate is low but typically much faster than time lapsed VCR systems.
The device is thin and palm sized. It's so compact and cheap (<$100) that you can just stick a tiny and cheap wired camera to it and hide the whole thing outside the door for example. That's even simpler than a wireless system. You can afford multiple units too. Instead of rotating the CAMS for recording, you can have one DVR for each CAM.
Night vision and motion detection
You don't really want a night vision cam alone because the video quality at dark will be poor even for military standards. Though a night vision cam can maintain video sync at total darkness with only a little faint red infrared LED illumination that usually comes with the cam. To record something decent you must add a low cost passive IR motion detector to trigger the flood lights for example. The switching of the lights will be seen as motion in the DVR with motion detection above.