Movement Sensors these days have lots of 'anti false alarm' technology built in such as white light filters and 'bug guards'. Here are the ones we've chosen from the marketplace to provide good capture performance and reliability.

The Standard PIR is ideal for most situations and looks neat and stylish. It can be easily adjusted for long or short range coverage.

The Quad PIR is for areas of extreme cold such as garages or extreme heat like conservatories where higher false alarm immunity is needed.
 
Our Pet sensor is a tried and tested model from trials we ourselves have conducted - one house has seven of these working with three cats very successfully!  It achieves it's success by a combination of PIR and Microwaves.

Finally the External PIR is weatherproof and can provide a chime when someone approaches the house. There is also a wireless version if wiring is a problem. It cleverly distinguishes between animals like foxes or badgers and humans.

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  Standard PIR               Quad PIR                 Pet TriTech             External PIR

Ideally you should have a movement detector in every room of your house, however this can be expensive and therefore as a recommendation they should be installed in all ground floor rooms with windows (except bathrooms or toilets) and perhaps a single detector on the landing along with any first floor rooms that might be easy to enter from outside from perhaps a kitchen extension.