In article ,
N. Thornton wrote:
Second be careful where you mount door opening detectors, as door
warping or wind can set them off. They are a big source of false
alarms.

The standard magnetic switch has to move a fair old way to trigger. It
would be some warping or wind movement that would cause a *properly*
fitted one to trigger.

Third cover your desired area with more than one technology. Only when
both detect an intruder do you want the system to go off. Most sensors
are prone to some cause of false alarm or other.

That was my thinking behind using door and window switches, pressure pads,
and PIRs. I don't think any one solution is the perfect one.

--
*If you try to fail and succeed, which have you done? *

Dave Plowman London SW 12
RIP Acorn