A switchable magnet (a non-electromagnet you can turn on and off). I have absolutely no need for one, but the science behind it blows my mind.
Amazon link: Magswitch MAGJIG 95 MagJig 95 Magswitch https://www.amazon.com/dp/B003FWERRC/ref=cm_sw_r_cp_apa_JxiWybT9TEWDM
I think adding on/off magnets could take these devices up to the next level.
https://www.amazon.com/Magswitch-MAGJIG-95-MagJig-Yellow/dp/B003FWERRC
Likely similar to these: Magswitch MAGJIG 95 MagJig 95 Magswitch https://www.amazon.com/dp/B003FWERRC/ref=cm_sw_r_cp_api_-zWCybTN5KD17