Hive make many sensors, when I googled Hive door sensor it showed a wireless contact as used to work intruder alarms, there are also motion sensors again seems they are designed to work with an intruder alarm.
The problem is working out what these devices will interface with as they will clearly not switch on a light without some other box of goodies.
I went for Energenie but same problem, until you buy it and try to set it up, one is not sure what it will do, and with mine it seems it uses IFTTT so if internet fails any connection using IFTTT will fail.
The device can clearly be protected from the elements, but you really need some thing which can be set to work in your environment and I have found PIR sensors vary a lot, with some being settable for sensitivity and even daylight, so I would think you want some thing which will not come on in daylight?
But any item with a 3 volt battery is not really a problem outside, it may get damp and stop working but there is no danger, as to damp that depends where it is, will it get direct rain or not, putting in a box it would still need to "see" something, be it a magnet or movement, and inferred can pass through some things visible light will not and also not through things visible light will pass through, and since designed to be used inside the house, it would be an advantage if it can't see through glass, so not triggered by anything outside.
So only way to find out is to try it.