I think alarm systems are usually well worth the investment. The key is to buy one that you will actually use, and can easily afford. For 90% of you, the basic alarm system you see on TV for $99 installed (and a monthly fee) is all you should need. Bad guys are normally not as sophisticated as they are depicted in movies and TV shows; a simple alarm will often make them choose someone else, which is all you really want. There was an old adage in the US Secret Service that we just had to make our principal the hardest guy to hit, so the bad guys will go somewhere else.
This is also true for car alarms as well as offices. A simple, easy to use alarm system that you can teach your family and office staff is best. I blame the alarm company salesmen for most of the unused alarms installed out there. They try and sell you a system that will stop a governments spy...one, that is never needed, and two, I have never seen an alarm or lock that with my government training and resources could not bypass.
The solution is a simple alarm system with minimal ways to malfunction. This means simple door contacts, window contacts, or a simple passive IR detector. The more intricate you make the system, the more likely it is to malfunction and that you will stop using it. To defeat a simple system takes almost as much effort as it does to defeat an expensive, complex system.
When I see an alarm system fail to work, 99% of the time it is because it was turned off, because it was broken in some way, or was too difficult to use. A panic button is the only thing I would add to the system, if your alarm does not already have one (most do).
If you have the option, you want the alarm hard wired in place, but the new wireless systems are very capable. If you are an apartment owner, the alarm may have to be a wireless system.
The next issue is the alarm itself. Some cities have a huge problem with needlessly loud or false alarms. They are very hard on the alarm installers, responders, homeowners, and neighbors. This is also why there are such heavy fines for alarms going off, up to $500 after a certain number of times. You really do not need to have a huge siren or blistering emergency sound going off. The bad guys can hear a simple alarm bell and often that is enough; they do not want to be there when police or security arrive, and they do not want neighbors taking note of them as they leave.
The next issue is who the alarm notifies, and how. Most alarms are monitored by the installing company with varying options. Simply instruct the alarm company how you want people notified. In most cases it is cheaper to have them call you or a family member first, and then, depending on the nature of the alarm, either they or you may call the police. Some simple alarms actually can be set to call your cell before proceeding with any further notifications, avoiding the company's monthly monitoring fee of $20-40 entirely. Personally I would use the monitoring company, and if you only paid $99 for the installation, then you probably will need to sign a contract for a year or more of monitoring.
The office and car alarms should be treated the same way. The use of CCTV is a big deal these days, but I would concentrate on the alarm for now; the cameras will be addressed in another post.
Remember, simple is good, because there is a better chance you will continue to use it, and there is very little to go wrong with the system.