🔑🔑🔑 we now stock 'Key Lock Switches'! These mechanical switches don't use a button, lever, or magnet to open and close the contacts. Instead, a literal key is used. This low-cost but effective key lock switch is nice and compact: you only need to drill a 12mm / 0.5" diameter hole in your mounting plate.

Insert the 'bike lock' style key and rotate it clockwise; now, the two contacts on the back are electrically connected. Rotate it back counterclockwise to disconnect the switches. You can remove the key in either position. It makes for an excellent 'On-Off' switch that requires the key to activate. 

If you want a version of this lock where the key cannot be removed in the On position,

Please note:  - each key lock order comes with the same keys. And it isn't hard to pick this lock, either. Think of this as a fun interface or minimal security setup where you aren't concerned with a skilled adversary.