Handcuffs... they might seem a bit crude, a bit simple, and they lack some of the allure of some of the longer-term leather wrist restraints, but aside from a kick to the groin, they are one of the few things that can render a sub helpless within seconds.
In movies and television you'll often see ways of escaping from handcuffs. Someone will pick the lock with a paper clip or a ball point pen or pull some acrobatic maneuver where they jump and swing their hands down under their feet so that their hands that were once behind them, are now in front of them. These generally illustrate handcuffs that were improperly applied.
Fun Facts about Handcuffs (and my non-factual thoughts about them):
-Professional grade handcuffs are double-locking. That is, once they have been locked into place, a secondary locking mechanism can/should be applied to prevent the cuffs from further tightening. This also makes picking the lock more difficult since the key must be turned all the way in one direction to release the double lock, and then turned all the way in the other direction to release the primary lock.
If they are double locked, it's unlikely that an individual could pick 1, let alone both of the cuff locks without the attempt being detected.
-Professional grade handcuffs usually have 2 welded links connecting the cuffs. While you can get handcuffs with more than 2 links (most novelty cuffs have 3 links), the standard issue handcuffs have only 2. High security cuffs are often hinged, limiting movement to 2 directions.
With a 2 link or a hinged style, the ability to try to pick the lock or perform acrobatics is severely limited.
-The highest security method of applying handcuffs is to handcuff the individual with the palms facing outward and the keyholes facing towards the elbows. This method limits arm movement and makes it easier for someone other than the wearer to unlock the cuffs.
Keeping the 2-link or hinged style in mind and with this method of application, very few people could actually reach the keyhole while being handcuffed. It's not impossible, but they're either very flexible or have extremely long fingers. Being handcuffed in this way throws off your balance a bit and leaves you completely defenseless.
-Prolonged struggling against metal handcuffs can lead to nerve damage.
Most metal handcuffs are better suited for short-term play than long-term wear.
I'm not sure why but I find it extremely exhilarating to be locked in handcuffs. It's not always for a reason that I find enjoyable, but it's not often that you feel that vulnerable, helpless, and defenseless. The audible click, the touch of the cold metal around your wrists, her hand grasping the back of your neck shoving you face first down onto the bed. It's a bit scary and intimidating but at the same time I'm then able to resign myself to the ride.