Here is a brief history of earlier designs:

Series 2 (no longer available)
1) Cost reduction in key tabs using water jet cutting which
allows more complex shapes.
2) Key larger than Series 1.
3) Key tabs TIG welded with base and shaft cap brazed together.
4) Motor coupling machined to motor centerline to reduce wobble.
5) Key held on with a tamper resistant screw on end of shaft.
5) Overload protector added.

Series 3 (no longer available)
1) Smaller key size to use standard shipping boxes and standard metal sheet size.
2) Three shapes added (rounded square, round and "Lilliput")
2) All seams TIG welded (fatique failures found in Series 2 braze welds).
3) Printed circuit board added for overload protection.
4) Billet base added to allow removal of key during automatic car washes.

Series 4 (no longer available)
1) Smaller oval shaped key size for less protrusion behind the vehicle.
2) Fixed position and free-spinning designs without electric gearmotors
added for lower cost.
3) Mounting option with frame under license plate.

Series 5 (no longer available)
1) Smaller oval shaped key size adapted to mount on rear wiper motor shaft.
2) Fixed oscillating design or custom one-way clutch for one direction rotation.

Series 6 (no longer available)
1) Series 3 design improved into 2-piece shaft for easier key removal.
This replaces the heavier and more expensive billet base design.
2) Vinyl boot included to cover drive shaft.
3) Change to smaller gearmotor with custom drive shaft assembly
which includes a large bearing ball bearing.
4) Added high intensity LEDs to replace license plate lights on some
designs for older VW Bugs and the Nash Metropolitan.

Series 7 (still in development)
1) Two-piece shaft design with larger diameter for a stepper
motor for lower noise and precise positioning when stopped
2) Added cost of drive electronics for stepper motor.
3) Still in development as of July 2009.

Series 8 (now longer available)
1) Smaller oval shaped key size for less protrusion behind the vehicle.
2) Custom design to replace the rear wiper motor.
3) Allows continuous rotation over the Series 5 design.

Series 9
1) Design like series 6 with 2-piece shaft for easier key removal.
2) Change to special design gearmotor (made especially for WindUpKey LLC)
with custom drive shaft assembly which includes a external bearing ball bearing.
3) Drive mount uses 4-piece design that does not load the gearmotor for
lower noise and quicker assembly.
4) Added high intensity LEDs to replace license plate lights on some
designs for older VW Bugs and the Nash Metropolitan.
5) Free-spinning design with dual bearings fits in same base and can
easily be upgraded to the motorized version at a later date.