There are a number of systems available.  But you should know that there is no such thing as a burglar alarm system that will make your house burglar proof 100% of the time.  However, a good alarm system can deter or detect most intruders and will afford an added measure of security when you are away from your house.

Some alarm systems are strictly perimeter protection and others use strictly interior protection.  The best system is usually one that protects the perimeter of your home combined with some interior protection.  The interior traps detect an intruder after he has entered the home or bypassed the perimeter system.

Preference for the desired level of security and type of system used depends entirely upon your budget and the design of your home.  The cost of an alarm system varies greatly, not only because of the equipment, but also due to other considerations such as the distance to the alarm company, local telephone rates, the amount of wiring required, the construction materials of your home, etc.  If it is connected to a monitoring service such as an alarm company central station, answering service, or other (telephone) facility, there is a monthly service charge plus telephone line and mileage rates.

Note: Many alarm companies offer services for a variety of emergencies such as burglar, fire, hold-up, medical, etc.  However, some alarm companies do not have the capability to distinguish the exact nature of the problem when they receive a signal into their central station. 

Following are some of the alarm components the company will probably discuss with you:

Perimeter Alarms

The basic home system is a simple closed circuit loop system consisting of contacts or screens on doors and windows.  Most are designed to ring a bell or activate a siren, and/or illuminate the area to scare off an intruder.  This will usually scare away most residential burglars.  There are several types of sensors used on perimeter alarm systems which include:

Magnetic Contacts
One of the most widely used residential devices is an electro-mechanical contact consisting of a magnet in one sealed enclosure and a switch in another sealed enclosure.  They are attached to doors, windows, transoms and other openings and wired to a central control box.

Screens
These special screens have an unobtrusive, built-in alarm wire.  They are usually custom made to fit the particular window to be protected.

Interior Alarms

Pressure Mats
Basically, this is a flat switch operated by pressure from a foot step.  They're usually installed under carpeting next to entrances, windows and stairways, and other areas where a burglar would likely travel through the home.  The mat may also be used for spot protection on the interior of a perimeter system.

Photoelectric Beam
Small, unobtrusive sensors are installed in hallways, large rooms, stairwells, and other similar areas.  Any interruption of the beam by a person walking through it causes an alarm.

Ultrasonic (Motion Detection)
Any movement within the protected area triggers an alarm.  The unit should not be installed where there is likely to be normal traffic in the house at odd hours, or where it is subject to large amounts of wind turbulence from open windows or heater or air conditioning vents.

Microwave (Radar)
This system is similar to ultrasonic - it detects motion in a specific area.  The difference is that the unit operates at a higher frequency and does not use air as a transmission medium.  Care must be taken in the installation to avoid accidental alarms due to the protection waves travelling beyond the required coverage area.  It must be FCC approved.  This unit is generally not recommended for home use.

Sound Units (Noise Detection)
These systems operate by detecting noise.  They are generally limited to use where there is low ambient noise.

Passive Infrared System
This system is a detection system operating in a mode similar to the photo-electric beam and can be applied to cover a room or hallway.

Capacity (Proximity)
This system is useful for protecting safes, files, cabinets, etc.  The major drawback of this system is that it will only detect a person several inches in proximity to the object being protected.

Closed Circuit Television
One system of some limited use to the homeowner is the TV camera.  This can be manned so that the homeowner can view who is at the door, or with some sophisticated systems and adequate lighting, can view the complete exterior. 

NOTE: You may also wish to consider having a fire alarm (smoke detection ionization) system installed along with your burglary system - have the company give you an estimate for both.  It is often economical to take care of it all at once.