Security of my AirBike is always a concern whether on display at an air show or when it is hangared.  Because of this concern and consideration for spectator safety, I made a lock for my ignition's master toggle switch.  By following the photo description below you can duplicate my efforts in about an hour of shop time.

In use, the spring-lock pin traps the toggle switch in the off position, the padalock's physical size prevents the pin from being removed.  Unlocking and removing the padalock allows the circular sping to be rotated 90 degrees to the unlocked position and the pin withdrawn.

Toggle ignition switch, spring-lock pin, padalock and two one-way screws were all purchased at my local Derby True Value Hardware Store.  Prior to making the sheet metal bracket I made a template out of paper to test for fit.  Note that the two in-line holes for the spring-lock pin are slightly off-center.  This makes it impossible to accidently lock the ignition in the ON position.
The guide bar of my table saw miter head was used to form the bracket shape.  I used .030 T3 aluminum, allow about .06 bend radii.
Simulated Installation
Less than $5 was spent on the locking mechanism shown here.

Although my ignition switch has a keyed lock,
(see Instrument Panel) it can be defeated.  This mechanical lock will prevent the Master Switch from being turned on accidentally.  This lock is a deterrent to accidents or crime, like all such devices it too can be defeated or circumvented.  Its intent is to prevent uninentional engine firing and deter theft of the plane.
Panel Page
Updated 03/09/04