Panic snaps are designed to allow instant release of a bound person in case of emergency. They are typically used to connect wrist cuffs to overhead fixing points. They are available at some sex shops and at all tack shops as they are used for horse lead training. The smallest size suited to horses will be sufficient for use with humans.
The risk of using carabiner style clips is that should the sub faint or loose consciousness then they will be left hanging from their wrists. The danger comes from the fact that these types of clip cannot be undone whilst under tension. This means that the top must support the sub's entire weight whilst they unclip the chains. The panic snap gets around this problem by allowing the clip to be undone while being under tension.
The reasons unconscious persons should not be suspended have to do with ease of breathing, stress on the heart from unusual stress lines in the abdomen and skeleton from the suspension, and from the possible damage to wrists and other joints which may occur while unconscious and suspended.
As the ordinary panic snap is inexpensive, a few should be regarded as mandatory toybox items.