I'm thinking the OP was hoping for a way to get at the duct from under the dash if removing the top grill isn't possible.... Doubt very much if the wire deal is gonna work, unless he removes the windshield. [/sarcasm]

 

No they are not. I have in my hand the packaging for PNY microSDHC card. On the back is an horse shoe msgnet icon with the words "magnet proof" under it.

 

Apparently they are a lot more durable than the last time I cared that much about them.
Hell, even hard drives can be dropped and are magnet proof now too (SSDs anyway!)

 

If you break into a SD what you find is a tiny circuit board with a tiny memory chip on it. They are a sort of EEPROM, not magnetic media. SSDs are just a large pile of similar chips.