I routinely use magnet bars to hold most of my hand-held turning tools, and occasionally have the tools become mildly magnetized to the point where it becomes annoying with the tool sticking to the rest and providing some resistance to movement. After sharpening, metal filings sometimes stick to the tools, which is also annoying!
The tool demagnetizers that are most effective are simply wire coils (usually around some sort of ferrous core) similar to a transformer, which create an intense magnetic field when energized with electric current. Back in the day, when audio was recorded on magnetic particles in "tapes" (reel-to-reel, cassette, cartridge, or the bizarre "8-track" format), one could readily scramble the magnetism in the tape by using a "bulk tape eraser" that does exactly what we need it to do to demagnetize turning tools. This is essentially a hand held, switched electomagnet coil. I routinely used these bulk tape erasers years ago when I was the station engineer for my college FM radio station, WCLH, in Wilkes-Barre, PA.
Energizing the tape eraser and then passing the electromagnet past the tool for about 20-30 seconds while moving the tape eraser randomly across the magnetized tool effectively de-magnetizes it very efficiently. Thicker tools sometimes need a second treatment, but in general, most tools can be de-magnetized with a single 20 - 30 second treatment, perhaps only once or twice per year, if that. Be sure to "rest" the tape eraser often to allow it to dissipate heat generated in the coils while in use.
You can sometimes find bulk tape erasers at garage sales, eBay, surplus sales, etc. usually for around $30 to $50 - far less than buying a new commercial demagnetizer unit. I have been using my demagnetizer on turning tools for over 10 years, and it still works superbly. (Mine is of the ca. 1978-1980 vintage - still going strong.) This is one of the tips included in my "Woodturning Gizmos and Gadgets" presentation that gets the most questions on how to get one of these units!
Rob Wallace