Most toys/gadgets/walkmans/tape players/electronic object that needs something to move will have a motor of some kind inside it. These can be easily turned into pickups thusly:
The inside of the motor will look a bit like this, with the magnets around the edge and the coils around an axle in the middle:
Drill a small hole inbetween the coils just about big enough to not destroy the magnets like what I did on my first attempt…
Do the same on the back so that the string can travel all the way through…
Wire up the + and – terminals of the motor to a socket…
Hey Presto!
The nitty gritty of why this works is pretty simple: electric pickups on guitars are just magnets and coiled wire, the vibrations of the strings create a fluctuation in the magnetic field which creates a very small alternating current in the wire. This is then sent off to an amplifier which comes out as noise. It’s all called Faraday’s law of Induction which is about one of the only things I remember from physics lessons. Electric motors work using the same Law of induction, so they’re built from magnets and coils just like a pickup, the only difference is how they’re utilised in everyday use, innit.
Vulpestruments 
That's a wonderfully insane way to make a pickup!
is there any reason the string couldn't just pass over the motor
While I was experimenting with this idea it was incredibly incredibly quiet when the string was outside the motor. I guess the magnetic field is a lot weaker on the outside. Also the coils around the axle were further away.
So really, just the closest you can get to the magnet and the coil the better!
Can I use a normal computer cooler for this Tom?
simple technology but very effective…
http://www.mrosupply.com
The new part was over $500 plus installation courtesy of Sundance Spas, whose parts are priced like Tiffany jewelry. electric bikes nz
Wire up the + and – terminals of the motor to a socket…
What socket?