Maybe burglar alarm technology could be used to detect stowaways? I guess false alarms could be avoided with careful design.
As someone who has worked in the security industry ... i would be cautious about placeing electronic intrustion detection systems in such a location.
firstly being an unpressurised, non temprature controled area, you have the possibility or indeed proberbility of leaving the components operating temprature range, with unknown results. even if you stay within temp range for the components, condensation is an issue, and can cause both false activations and nil activations
secondly, there is a definate proberbility of both false positives and false negitives in the detection system its self, .. assuming that it *never* leaves is design paramiters.
false postives are annoying and would largely cause air/ground crew to learn to ignore the alarm if possible. False negitives would result in no alarm activation, should an intruder decide to enter that area.
False positive/negitive statuses become more likely as the equipment ages as well.
the net result would be a loosening of the guard against stowaways, on the blithe assumption that 1, the alarm will get it, and 2, when the alarm activates, its a false alarm
i would support more and greater depth ground checks by .. well humans.
If gear bay doors cannot be signaled open for inspection, maybe this should be raised with the manufacturers?