Back to the hard drive discussion - I would destroy old drives by taking them apart and bending the platters such that the oxide coating cracked off. Read that! You can imagine my surprise when I found out about glass platters while trying to bend it. Still couldn't read it afterwards.
My reason and reward for destroying them this way, I kept the neodymium magnets. I have more than a lifetime supply, and find new uses for them all the time.
And, did you know you can hook a USB floppy drive to an Android phone using a USB On-The-Go (OTG) cable? I did this for kicks, and read data from a floppy. I forget if I was able to write to it. Also works for USB keyboards, mice, memory sticks and, I think, hard drives.
A quick look on Amazon shows OTG devices for iPhones, I've never tried one.