Self-bondage Challenge
So, you're the pain-slut who accepted this challenge. I wouldn't, but to each their own. My only concern is making sure that if you do this, you do it properly and safely.
Start by testing the handcuffs. Attach each cuff one at a time to one of your wrists, and then use the key to unlock it. They need to unlock easily, so that you could unlock them even in an awkward location, like hands cuffed behind your back. If they are so stiff that you think you may have problems doing this, then get a looser set of handcuffs. Do this test enough times so that you are certain that there is no trick to the cuffs, and that you will be able to unlock them when the time comes.
Next, get naked! Everything must be removed, even jewelry. You can first unplug computer cameras, close any curtains, and take any other precautions you need to make sure that no one sees you this way. In fact, I insist that you do so. This isn't a fear-of-exposure tease, it is a complete-what-you-started tease. I don't want to risk a nosey neighbor seeing your dilemma later, and coming to your rescue.
Next, wrap your belt around your waist and buckle it. It should not be so tight as to cause you discomfort, but it must be tight enough that you absolutely cannot slip it off yourself without first unbuckling it. Try it now, and if you can slip it off, then put it back on and buckle it a little tighter.