I broke my personal rule of always clipping my belay device to the rear of my harness when not in use. It was a cold day and I was wearing lots of bulky layers which made it hard to check the front of my harness. Looking down at my belay device I assumed it was clipped to the strong belay loop when in fact it was simply clipped to a plastic gear loop. I began abseiling and immediately noticed it felt wrong (all the weight on the waist belt and none taken by the leg loops). I pulled back over the top of the crag and was shocked to realise I had just dangled 25m above ledges on a plastic gear loop.