I think IR sensors set off an alarm when the "picture" of IR changes. I have
done some testing with home security alarams, and if you really move slowly,
the alarm will not go off.

Haakon

"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.

Jean Dufour
Montreal, Qc

John Smith wrote:

Looking for some advice on the most appropriate sensors for a moored
cruiser. I have switches on the door, the hatch and some windows, I
have
two infra red motion detectors and a pressure mat.

Are the IR detectors any good on a boat that sways a lot in the wind
etc?
Any other options?

Thanks in advance

After trying various moored boat setups with false alarms, I found that an
ultrasonic motion detector wired in series with an IR motion detctor works
PERFECT. No false alrams ever, and will alarm if a person intrudes. The
ultrasonic units are considered obsolete, but you can still find them on eBay.