I was a partner in a company that made and installed security systems. There are two basic kinds of alarm systems, local, where the alarm rings only at the premises (a bell or siren outside and inside the building, for example) and remote, where the system contacts law enforcement through an autodialer or via network when an intrusion is sensed.
Infrared heat and motion sensors, video, remote listening and pads in the floor can all be used to detect intruders. The technology for these gets better every day. However, technology, as always, doesn't cure all ills.
The local security system for a home or business has the same problem that car alarms have - when you hear a bell or siren it is generally more of an annoyance than a signal that someone is in trouble. How many times have you heard a car alarm and thought, "What an idiot!"? You don't think "Someone's car is being tampered with. I need to do something!"
Similarly, when people hear a local alarm they assume someone else has called the police. The local alarm has some value in that it might scare an amateur burglar away, but a pro might not care. A pro either defeats the alarm ahead of time, or destroys the annuciators (things that make noise.) A burglar can shove a screwdriver through a speaker or siren, or foam a bell by injecting fast setting foam plastic into its housing.
Remote systems that dial law enforcement can be more effective than the local, self-contained system. The problem with this configuration is that false alarms (system set off by mistake by a family member, by a pet, by a contractor) also dial the police which is more than irritating. Police will fine homes with false alarms and may stop responding altogether to chronic offenders. The City of Albany, Oregon, for example estimates that 90% of all alarms are false! False alarm fines in that town start at $50 and go up from there.