| This article outlines how and where to fit vibration (aka shock, inertia) detectors.
Introduction
The simplest way of protecting windows and doors is to fit inexpensive magnetic contacts. However, there are a few disadvantages in using magnetic contacts.
- A contact has to be fitted to each opening light which can result in complex and messy wiring.
- Magnetic contacts do not detect the removal of glass from a window or a panel from a door.
A more elegant solution is to fit vibration detectors. A single vibration detector can cover a multi-paned window with several opening lights.
And, for doors in particular, a vibration detector with an integral magnetic contact is available which will alarm if either sensor is triggered.
How vibration detectors work
Early detectors were mechanical devices comprising either a ball and cup arrangement or a weighted spring arrangement. Because these produced a transient signal an analyser interface had to be fitted. The good news is that modern vibration detectors are purely electronic devices, and do not need an analyser. Modern devices are tuned to the typical frequencies produced by an attempted forced entry.
Positioning
When fitted, the detector should detect an attempted intrusion but not detect road vibrations (heavy lorries passing etc.) or window cleaning. In general this is achieved by fitting the detector to the centre of the top or bottom edge of the window frame and then adjusting the sensitivity. A single detector will typically cover a 3 metre x 2 metre window.
Commissioning
Because the detector must be fitted firmly to the door/window frame it is necessary to pre-determine the fitting position. In general, the detector is best fitted at the top or bottom centre of the frame for windows, and on the frame adjacent to the lock for doors. When the detector has been firmly fixed the detector's sensitivity is adjusted such that it triggers when typically hit with a medium bang with with a rubber hammer or closed fist.
Vibration detectors have 'Comfort' LEDs, and these should be enabled or disabled as required.
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