This invention is a knife sheath that holds the knife inside the sheath with a permanent magnet. To temporarily deactivate the magnet, simply neutralize it with an electromagnet. All you have to do is press your index finger to a small heat sensor on the side of the sheath, which activates an electromagnet and neutralizes the permanent. The electromagnet is powered by several watch batteries. This arrangement makes removal an incredibly swift and ergonomic movement. Grip the hilt with your pinkie, ring, and middle fingers, and your thumb, touch your index finger to the heat sensor, and pull it out with no resistance. The heat sensor is my preferred off-switch because it prevents anything else bumping against it from dislodging the knife.
This invention is intended as an improvement over sheaths which use a button snap to hold the knife in place, because those damned buttons can be unsnapped by catching on your coat, or on part of a chair when you stand up after sitting. I also dislike friction sheaths because you have to pull against resistance, which I really dislike. Perhaps, instead of battery power, it would best be rechargeable. Or both. I'd probably sell a few different versions for more market vesatility.-- 21 Quest, Apr 24 2009 Electro magnets would just suck the battery dry in no time. Why not go with ordinary permanent magnets?-- zeno, Apr 24 2009 what [zeno] said. of course, you could use electromagnets to neutralize the permanent magnets when you press the sensor you describe.-- sninctown, Apr 24 2009 Zeno, because I don't want to have to pull against the magnets to release the knife. What I'm going for is frictionless release.
sninctown, I hadn't thought of using them to neutralize permanent magnets. I'll amend the post accordingly, thanks.-- 21 Quest, Apr 24 2009 Maybe use a switchable permanent magnet mechanism, as used in magnetic hold-down devices used by woodworkers, instead of the electromagnet?-- notexactly, Jan 28 2016 How about a friction wheel that unlocks when the user grabs the hilt? It doesn't have to be hard to do, just a small amount of pressure along a metal latch on the knife would suffice.-- Voice, Jan 28 2016 I'll go you one better - something that doesn't need a battery.
Have a catch or lug that secures the blade in the sheath, held in place with a spring, which is metal or has a magnet on it. Externally on the sheath, have a tab or switch or whatever that moves a magnet close enough to the catch so that it pulls the catch clear of the knife, releasing the blade. Works a lot like contactless waterproof switches seen on high end underwater torches/cameras etc.
Should be devilishly reliable, simple, and very smooth.-- Custardguts, Jan 28 2016 random, halfbakery