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A DVR camera is a security system which links one or more cameras to a digital video recorder. It's main advantage is that it can record for much longer periods without the need to change tapes. The technology also means it is possible to review footage immediately while continuing to record.
If you've ever seen a device such as a TiVo®, you'll be able to get a good idea how a DVR camera works. The input video is recorded to a hard drive rather than a video tape. Instead of connecting a cable or satellite box to the DVR, the user simply hooks up one or more cameras and records the feed.
Using a DVR camera overcomes one of the biggest limitations of a cassette-based recording system. Usually even the largest video tape recording at the slowest speed will be limited to eight hours recording time. This means that it's impossible to use the system for extended periods without somebody being on hand to change the tapes.
It's much easier to run a multi-camera system with a DVR camera. With video tapes, you either need a separate recorder for each screen, or must use a split-screen system which means the picture recorded from each camera is smaller and thus less detailed. A DVR can process full-screen feeds from multiple cameras simultaneously.
Because a DVR camera records digitally, it's much easier to archive recordings in case you need to refer back to them later on, for example when providing evidence in a criminal investigation. The size and relatively low capacity of video cassettes means a week's worth of recordings can easily fill an entire shelf. Many users are thus forced to reuse tapes and only keep a limited amount of footage. Footage from a DVR camera can be stored on DVDs, meaning an easily portable 240-disc carry case could contain archives from two full years of recordings. The discs are much more portable than cassettes, meaning they can be moved off-site for extra security.
Another major advantage of a DVR camera system is that you can play and record at the same time. With a cassette system you could not watch recent footage, such as checking on a report of an attempted break-in, without either waiting until the tape was full, or switching tapes. A DVR camera allow you to rewind and watch footage from any point from a second ago to as far back as the hard drive recording covers.
There are also some security advantages in the way a DVR camera is powered by a computer. You can set password protection so that anyone stealing the hard drive would be unable to view the footage. Some models can even be connected to the internet and set up so that if an alarm is triggered, the footage recorded just before the alert is automatically e-mailed to another computer such as your home PC or even to the police.