The first thing you need to consider when having CCTV installed is, what am I using it for?
H&S of employee's is one of the most key factors and in some cases can also reduce the cost of insurance.
Whatever kind of CCTV you go for, think about the cost, i.e. what is your budget?
If you're using it for monitoring staff, I'd have to suggest using a reasonable camera, anything with a fixed lense is useless. Internally, we tend to install 4-9mm lense cameras, gives a better clarity of picture of staff, rather than the surroundings, and vice versa (pending on settings of course). This of course really depends on the size of your property.
Also, in my honest opinion stay away from any of the older formats of Jpeg or Mpeg DVR's. Majority these days are H2.64 which is a compressed file (10x better than Mpeg/Jpeg compressed file systems).
Basically, when you're watching footage remotely through the PC or Internet, the older systems use frames per second (FPS) this can cause issues where you can end up with a person stood in one position, and the next frame they're about 3 foot away from the previous position, thus loosing footage to a degree. Whereas H2.64 systems compress the files so tightly that even though they are still technically classed as FPS you don't loose anything at all while watching through a PC.
If you're going to go for a 4 camera system, may I also suggest that you purchase an 8 channel DVR with minimum of 1TB of memory on the HD (hard drive). If for any reason you decide you want extra cameras installing, you've got the ability to add imediately rather than having to fork out for a replacement DVR from the getgo.
Always ensure your DVR is locked safely away, either in a server room or locked office out of sight.
If for any reason you have reason to believe that you are being "watched" by thieves, then buy a second DVR, connect them both together and hide one away out of sight so that only you and you alone know's where it is, loft space or in a suspended cieling is always the best place, that way, if someone does gain entry, and remove the DVR you'll have a second one recording their actions.
If your budget allows for it, get a system installed by a small reputable company, no offence to the larger companies out there but stay away from them, they can be over priced and in some cases will always try to tie you down to a service contract which in most cases for CCTV systems isn't really needed, if it's fitted and used correctly, it should last at least 5 years without any issues.
There is one company that I know of that claims that all DVR's only has a 3 year life expectancy, and goes into a lot of detail about how it can cause major issues... what they actually mean is that the equipment has a 3 year gaurantee, what they do is come and swap out the DVR thus charging you just before the 3 year mark, and they send it in for "repairs" if required, and they have it returned and then they install it elsewhere, with a new 3 year warranty from the manufacturers.
This particular company did the above to a customer of mine, and charged the company over £1200 for doing so, the Director of the company went online and found the very same DVR online for just £399, he was extremely annoyed to say the least, as he'd basically been charged £800 for someone to come in, unplug one DVR and plug in the new DVR, they didn't need to make any changes to the settings as majority of them come preset to a standard recording standard which majority of people actually use.
Lastly, some people automatically assume that if you have CCTV with the ability to use remote viewing, all you need to do is hook it up to your PC, although this can be correct for most products, you need to consider getting a static IP address from your service provider. should only cost about £5-£10 per month on your monthly bill.
If you don't get a static IP, there is always DDNS, although a lot more fiddly to sort out, always ensure your IT department is available to set you up for this, not all CCTV installers like to mess about with companies computers for fear of buggering their set up... firewalls can sometimes cause major issues if not set up correctly.
