DD243 should not allow these detectors

I read with disbelief the item in the latest BT redcare newsletter on DD243 revisions that states that units with two motion detectors in the same housing (TMD units) are to be allowed to provide sequential confirmed signals unless future false alarm rates become unacceptable.

My main concern is the fact that these units will incorporate only one power feed and that they are inherently more prone to false alarms than separate detectors. Common causes will be:

RFI causing blip in power to detector resulting in both paths signalling;

Large moth/spider/mouse etc near to detector causing both “curtains” to activate;

Unit processor failure or power connection dry joint/ loose connection causing activations on both paths;

Air conditioning/blowers etc.

All of the above would cause most standard detectors to activate, but would not cause a sequential confirmed alarm as it would generally be a local problem to that detector. There is no way that use of these detectors should be permissible if DD243 is truly to mean anything.

The whole point of DD243 is to reduce false alarms by the use of good procedure, best practice and the activation of two separate detectors. I feel that the industry acceptance of these units is based on satisfying the commercial objectives of certain manufacturers and some installers who want to provide DD243 on the cheap.

This sort of capitulation is, quite simply, wrong. The industry needs to take the right decisions based upon fact and probability and not on the commercial requirements of individuals who do not realise or care about the technical issues involved.

It is a great shame that the industry has not had the courage to unequivocally oppose these detectors and I find it astonishing that ACPO and the ABI are clearly prepared to accept them.