I used a carabiner attached to the belt loop to carry the keys. While this worked fairly well, my keys were always tucked under my shirt. I've tried different types of key holders lately and each has its pros and cons. A belt instead of a belt loop allows me to carry my keys over the hem of my shirt, but I've found that this can be done with two hands if I put the keys back on. Keys keep falling off. It's good if the keys aren't dangling under your shirt.
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