Shock sensors are devices placed on a window or door frame which detect vibration, i.e. if someone is banging, jiggling or attempting to force open the window or door the sensor picks this up and causes the burglar alarm to activate. They are also called inertia sensors or vibration sensors.
Hkc combined wired shock sensor and contact
Hkc combined wireless shock/contact
Magnetic contacts are devices placed on window or door openings which only detect when the window or door is opened, i.e. they do not detect the glass breaking, or someone using force to burst it open. The magnetic contacts we use would be a good brand such as Honeywell.
Simple magnetic contact
Passive infrared detectors are devices which detect body heat. They are placed in the corner of a room and detect if anyone moves in that area which causes them to trigger the alarm. They are also called motion sensors, beams, PIRs. We always use a good brand such as Honeywell for prewired or Hkc for wireless situations.
Hkc motion sensor
Which is better? Normally it is best to alarm accessible windows and doors with at least shock sensors and ideally with magnetic contacts also. Doors should always have both shock and contact. The ground floor windows and doors are the most likely to have someone use force to break in which is detected by the shock sensors.
Inaccessible windows such as upstairs windows may not need to be alarmed at all, or perhaps with magnetic contacts only.
There should be at least 1 passive infrared detector in the hallway as backup. The passive infrared detector is used as a backup to the shock sensors and contacts in the unlikely event that someone gets past the perimeter.
Some installers will quote for motion sensors only which makes for a much easier installation from their point of view and perhaps they can give you a cheaper quote however the drawback is that the burglar would already have to be inside your home before the alarm activates!
Here is a video demonstrating shock sensors, magnetic contacts and a motion sensor in action.