I posted this in response to a question on the Tekumel Facebook group: "How do low-magic zones affect magic weapons?" Sharing here for the Bethorm community.
Regarding magical swords (all magic weapons really, plus magical armor and shields), here are my impressions from working through conversions from S&G and Gardasiyal to Bethorm, after reading Barker's mechanics very carefully to try and puzzle out what he was trying to model:
Most minor 'magical' armaments are only considered 'magical' because they're so much more effective than the Chlen-hide versions that folk are familiar with. Steel items (and some other exotic materials - but not copper, sorry Sarku) are inherently better in combat than Chlen-hide, and so they get a slight "+1" bonus simply because of that. And the ancients knew of techniques for working with steel etc. (alloys, tempering, etc.) which enabled them to make 'em even a bit better than that. *That* kind of 'magic bonus' isn't going to be affected by a "non-magic" or "low magic" zone, because it's not magic in that sense, it's actually craftsmanship and physics.
Then there are spells which *enhance* armaments. These can be disenchanted, and so I wouldn't be surprised if the magic bonus got 'suppressed' within low-magic zones (but I'm not *certain* whether that happens). And keep in mind that *some* of the bonuses on a weapon or piece of armor that has been 'enchanted' may still just be inherent from the metal it's made from, or from non-magical craftsmanship. So as a general rule of thumb, I allow 'magical' armaments to retain 1/2 of their 'magical' bonuses (rounded up), even in completely 'dead' magic zones. To the best of my knowledge, low-magic areas don't *dispel* enchantments, so full potency would return upon leaving the zone.
And then there are *demon-possessed* armaments. I haven't been able to find much canon material on what's exactly going on with those things, so I'm going to have to go very speculative here. I've toyed with the notion that the "demons" are actually high-tech artificial intelligences, and not other-planar entities. It seems plausible. But the fact that (by Barker's mechanics) they can cast spells and have theological allegiances makes me doubt this. So then the question is, what does it *mean* to have an other-planar entity "bound" to an item? It doesn't seem to be physically "in there", like a genie in a bottle, because I've seen no evidence that the demon can ever physically emerge. Is it just the demon's *consciousness*, then, like the SF concept of uploading a person's mind into a computer? That also seems plausible, especially since I've seen no evidence that such 'bound demons' can ever escape or even bargain for their freedom. If they *only* exist as a consciousness in the item, then they have nowhere to escape *to*. In that case, whether the demon's ability to think and communicate is suppressed by a low-magic zone would depend on whether the function of its mind within the item is otherplanar/magical, or merely uniplanar/physical. I don't see why it'd have to be magical; low-magic zones don't interfere with *human* minds, after all. The demon's *spells*, of course, would be weakened or blocked by a low-magic zone, the same as a human's.
BUT, there's another possibility, which is that the demon isn't an 'upload' - but rather, that the item merely contains a conduit through which the demon can be contacted, and through which it can exert influence (such as casting its spells). It wouldn't need to 'escape' because it isn't 'trapped'. In *that* case, a low-magic zone would presumably interfere with that conduit. Interestingly, this would imply that more than one item could be 'connected to' the same demon. I've never heard of that happening, though, so I personally lean toward the "uploaded consciousness" interpretation.