Chisel the huge ferrite disc magnet off the back of a large dead speaker (if it wasn't dead before you started chiselling, it sure will be when you've finished) and you'll have a magnet with only about 1000G field strength, measured at the peak strength areas on its poles. It's a ferrite. That's all you get.

But big speaker magnets commonly weigh more than a kilogram and are several inches across. The peak strength areas at the poles are thus already a few inches away from the middle of the magnet's field. In this case, you can move another few inches away and still have 1/8th field strength.

So if you wave one of these big magnets over a pile of nails, they'll leap up to stick to it from several inches away.

Take a 1-Tesla-field-strength neodymium magnet the size of a button, though, and the peak field areas on the outside of the magnet will only be a couple of millimetres away from the middle of the field. Now moving just another couple of millimetres away gives you 1/8th field strength. Field close to magnet stronger; field far from magnet weaker.

That said, 1T power is still pretty darn impressive. Most current-model Magnetic Resonance Imaging (MRI) machines only have about 1.5 Tesla field strength, for comparison.

The reason why an MRI machine is a giant contraption that needs liquid nitrogen cooling, rather than a neat little metal-plated lump that you can buy over the Internet, is twofold. It's partly because the MRI machine is also a sensitive radio receiver, detecting the radio-frequency energy emitted by the magnetic nuclei in the patient's body when they interact with a strong magnetic field. But it's mainly because a 1.5 Tesla MRI machine is creating a 1.5 Tesla field over a large enough volume that a patient can be stuck into said field.

By the same token, junkyard car-lifting electromagnets only have about 1T field strength, but they generate that field over a big enough volume that their total lifting capacity, for conveniently steel-bodied cars, is massive. The coils under their protective armour draw at least a few kilowatts, and maybe considerably more - 20kW isn't out of the question for a big car-lifter.

You're not going to be lifting any Toyotas with a five buck magnet from anywhere. Nails will hop up only about an inch to hit the strongest of the magnets in the ForceField grab bags. In contrast, ferromagnetic objects of all types will fly across a room to make friends with an MRI machine, as occasional tragic accidents attest.

Because of their limited field size, small neodymium super-magnets like these ones aren't actually much of a problem to deal with, at least as far as messing up your monitors and erasing your credit cards and wiping your video tapes and being hit by flying spanners goes.

Yes, when I had one in my back pocket, I at one point found myself unexpectedly attached to the washing machine. But the rapid diminution of the field strength means that you can hold the strongest of these magnets - the three spheres end-to-end, for instance - in your hand and wave them around a mere foot and a half from a computer monitor, and notice only slight image distortion and discolouration. Move the magnets further away and the effect vanishes.

Touch those same magnets directly to the screen, mind you, and they'll magnetise the heck out of the shadow mask and leave you degaussing until practically all of the world's cows have come home, had a nice sleep and gone away again. I own a degaussing wand...

...but I am not confident enough of my skill with it to deliberately Magna-Doodle all over a monitor just so you can see what it looks like. Sorry.

Quite big rare earth magnets can be had, if you want more field range. There's this one, for instance, which only has about 1.1 times the volume of a ping-pong ball, but which ForceField just won't sell you unless they're satisfied that you're not going to crush, blind or mangle yourself with it.

As far as terrestrial magnetic fields go, 1T is quite strong, but it ain't much by the standards of the universe. Neutron stars and pulsars (which are spinning neutron stars) have magnetic fields. If they were made of nothing but neutrons then they wouldn't, but they've also got superconducting superfluid protons and various other exotic forms of matter, so they have.

They get just about the whole magnetic field of the normal star they once were, squished into their city-sized diameter.

The magnetic field strength on the surface of a pulsar has to be at least several million Tesla, and may range as high as a thousand million Tesla. That's more than strong enough to seriously deform electron orbits and make matter do very, very strange things, regardless of whether it's the sort of matter that normally cares about magnetic fields or not.

This magnetic field would certainly kill anybody who tried to land on a pulsar. Except for the fact that they'd have been very conclusively killed already by radiation and/or gravity gradient. Plus, landing on something that's spinning fast enough that its surface whips past at kilometres per second - in some cases, thousands of kilometres per second - presents a bit of a challenge in itself.