You can use this reflective snap band on your arm, or on your ankle instead of a traditional trouser clip.
Just roll it out flat then tap against your arm or leg and it 'snaps' to fit. The whole band is reflective - and you can never have too much reflective material on you, especially if you're commuting during dark winter mornings and afternoons.
I used it as a trouser clip and though it didn't feel as substantial as the much wider Velcro-fastening Lycra one I normally use, it didn't come undone and nothing got tangled in the chainring. The soft, brushed material on the inside means you can wear it comfortably against your skin when the weather's warmer, and it rolls up really small too, so you can pop it in a pocket - the only real problem being you have to remember which pocket...