I want to firstly thank everyone for the advice offered.
I proceeded to obtain a PIR motion alarm, specifically the MA80 Mini Alarm for UniquExceptional. This particular unit includes a land line connection to a phone
line, not much need or use for me on a boat, but it's there...For a boat moored in at a dock
, with a phone
line, it might be (it can dial up to 3 phone numbers when triggered). I don't recall
(and did not pay much attention) if they offer a unit identical more or less, without the phone capability (for which I likely paid more). Cost of the unit on Amazon was US $28 (free shipping
with Amazon prime).
I tested it at home today, and worked as expected. Program a 4 digit code to disarm it. Press "0" to arm, then you have 30 seconds to vacate it's detection zone. It indicates a 140 degree horizontal angle of detection. It detected me approaching from 15-20 ft away, and i had about 15-20 seconds to disarm it with my code. Once it triggers, it turns off (before or after sounding) immediately upon entering the code. It did not detect me (waving a hand) above it, directly and within a foot or two horizontally above. It indicates a 70 degree vertical angle of detection, so a foot or two away intersects at a height of a foot or two above.
Interestingly, it is just above freezing outside where I tested it, while fully clothed and in a winter jacket. It detects based on IR detection only (motion of heat, not just visual motion) and detected that small delta
of heat emanating through my clothes (or the very small territory not clothed). That suggests it should do fine detecting human heat differential in a tropical climate, but I'll know better once there.
It sounds within about 15 seconds of detection. Reviews
have called the alarm "ear splitting". I tried it with ear protection, it was audible through that, and when I removed the ear protection it was sufficiently loud, but I would not say quite "ear splitting", unless maybe you test it indoors.
I verified that it does not just sense mechanical motion, by waving a hose in front of it while I stood behind. It did not detect the hose at any angle within a distance of a foot or two (essentially right in front of it). It should not, based on PIR technology and my verification, trigger for motion of a wave, a dinghy, or a line dangling from the boom, etc.
My plan is to try it either on the forward leg of the cockpit table, facing the companionway
, or on the aft end facing the transom. It could be placed also in an aft quarter of the cockpit facing the companionway. I'll assess when I am physically at the boat (a charter). One other option in mind is to hang it on the companionway top hatch board, secured with an angle iron over the hatch board and into the cabin under the sliding hatch. however I place it, the goal is to catch an intruder within the 20 sec trigger and secure it only sufficiently that the intruder cannot quickly or easily dismantle it (e.g, toss it overboard). In any case, it has two mounting holes and screws on the back, to which I plan to attach a small board that I can screw to an angle iron or secure somewhere in the cockpit.
We sail in about two weeks, in the Windwards, I'll report back on experience around mid March.