Anyone who has been around RC aircraft is aware of the danger of getting tangled up with a prop. Modern high-end props made for electric flight can be nearly razor sharp, and even the rubbery cheap sort will cut through skin like a knife through butter once they're up to speed.
Keeping appendages out of the arc of the prop of an ordinary RC airplane is easy (but people nevertheless sometimes hack themselves up). With a quad, hex or such, however, it's much more difficult to keep clear. On my hex for example I have to reach right through the prop arcs to connect and disconnect the flight battery, start the camera, and so on. I use "throttle hold" on my Tx which protects against an accidental bump of the throttle stick, but as we all know machines sometimes seem to have evil plans of their own!.
Working on the bench with connected flight batteries is particularly dangerous. The standard advice is to remove the props first. But that is a PIA and so doesn't always get done.
Today I needed to power up the hex on the bench and just didn't want to pull the props. But rather than be uncomfortable and unsafe I made a simple device out of a length of cord that keeps the props from spooling up in the event of any sort of electron rebellion. I like this so much that I'm going to use it routinely at the field and on the bench. Hope someone else finds it useful too.