"Jean Dufour" wrote in message
...
IR sensors will detect the heat generated by someone in your boat. It's
ultrasound sensors that would be trigered by the motion of something
moving
in your boat. But what if the boat's interior is heated to higher than the
body's temperature on a sunny day? I dunno enough about this to risk a
categoric answer. But I GUESS it would generate a false alarm.

They don't. IR sensors 'look' into the area in sectors, like A-B-A-B-A-B and
reacts on the difference between A and B. If the environment temperature
changes, both the A and B sectors change, hence no alarm. If someone walks
through the area, A changes, then B, then A again. The alarm trigger is set
to the amount of change and the number of changes. It can be set so
accurately that it wouldn't alarm on a cat or a small dog, but only on a
large enough body, like a human. Because is reacts on changes, it also does
not alarm on a sudden sunshine through a porthole.

Meindert