when you put it near a magnetic strip which is stuck onto an item in a shop, and it disables it? Is there such thing or am I just talking through my ass here?

you mean what do the people behind the counters of like, GAP and Urban Outfitters etc rub the tags of clothes on to make them not sound the alarm when you go out their doors? (they seem to just rub it on the counter-top)

.....is that what you're asking about? because i have no idea what it is

Very similar to this but it was some kind of magnet of some sort, which could be made at home.

You mean like the de-magnetizing things they have at registers that they pull the item over? No idea how you would go about making one.

An S3 handkey, however:
http://www.alphaworld.com/videos.asp
http://s156.photobucket.com/albums/t33/jesusnachos/